Chevrolet Corvair

The Chevrolet Corvair was a rear-engined automobile produced by General Motors from 1960 to 1969. The Corvair was offered in a wide range of body styles (such as a four-door sedan, coupe, convertible, station wagon, pickup, panel van, a window van called the Greenbrier) and featured an air-cooled engine, which was unusual for American cars at the time.

The Corvair remains one of GMs most unusual creations. Design began in 1956 under the auspices of Ed Cole, and the first vehicles rolled off the assembly line in late 1959 as part of the 1960 model year (in which it was named Motor Trend magazine's Car of the Year).

The Corvair — like the Ford Falcon, Studebaker Lark, Rambler, and the Plymouth Valiant — was created in response to the small, sporty and fuel-efficient automobiles being imported from Europe by Volkswagen, Renault and others.

The Corvair was part of GM's innovative A-body line of cars, but this was by far the most unusual, due to the location and design of its engine. It was a rear-engined vehicle in the style of the Volkswagen Beetle and the Porsche 356 Speedster. The "trunk", on the other hand, was in the front of the vehicle, while the spare tire was stored above the flat engine, saving trunk space.

The entire line (which eventually grew to incorporate sedans, coupes, convertibles, vans, pickups and station wagons) initially shared an aluminum, air-cooled 140 in³ (2.3 L) flat-6 engine. The first engines produced as little as 80 hp (60 kW), but later developed as much as 180 hp (134 kW). For 24 hours, the Corvair was tested at the Riverside International Raceway in Riverside, California, one car did a roll but the other did the 24 hour drive and only lost a quart (1 L) of oil (Source: Riverside Raceway Palace of Speed by Dick Wallen)

The first Corvairs (1960 – 1964) were factory equipped with an ignition lock wherein it was possible to start the car and then remove the key. Doing so in Southern California and being caught by the Los Angeles Police Department was a guaranteed ticket to a weekend in jail.

History

The Corvair name originated as a fastback show car in 1954, which, like many Chevy concept cars of the period, were based on the Corvette, including the Chevrolet Nomad and Chevrolet Impala. The design was championed by Ed Cole, Chevrolet chief engineer in the early 1950s and general manager in the late 1950s, as an answer to the growing popularity of small, lightweight imported cars.

The early 1960 models were conceived as economy cars, and had boxy styling, basic trim, and few amenities to keep prices down despite the relatively expensive and unique powertrain. A novel feature available for two-doors was a fold-down rear seat, included on some higher-level models. Passenger compartment heat was supplied by a gasoline heater mounted in the luggage compartment. The line quickly grew from plain, four-door sedans with bench seats (the base 500 and slightly more upscale 700) to the Monza 900, a two-door coupe with bucket seats and plush trim introduced late in the model year. Optional was a more powerful engine rated at 95 horsepower, thanks to a more radical camshaft and low-restriction exhaust. Despite its late introduction, the Monza sold 12,000 copies, making it one of the most popular Corvairs.

1961

For 1961 Chevrolet added an optional four-speed manual transmission to augment the standard three-speed manual and optional two-speed automatic. The Corvair engine received its first size increase to 145 in³, courtesy of a slight increase in bore size. The base engine was still rated at 80 hp (60 kW) when paired with the manual transmissions and 84 hp (63 kW) when mated to the optional automatic transmission. The high-performance engine was rated at 98 hp (73 kW). The standard heater was changed from the gasoline heater to engine cooling air ducted into the passenger compartment. The gasoline heater remained an option through 1964.

A station wagon, the Lakewood, was also added to the lineup in 1961, and it contained a total of 68 ft³ (1.9 m³) of cargo room — 58 in the main passenger compartment, and another 10 in the "trunk" under the hood. Engine heat and gasoline odors migrating up through the floor of the station wagon proved to be a persistent problem, and the wagon was relatively short-lived.

That same year, Chevrolet also introduced the Corvair 95 line of light-duty truck, which used the Corvair driveline and were forward-control, with the driver sitting over the front wheels, as in the Volkswagen Type 2. The Corvan model was available in a myriad of configurations as both a panel van and a window van. There were also two models of pickup available. The Loadside was a fairly typical pickup of the era, except for the rear engine, forward controls, and a strange pit in the middle of the bed, The more popular pickup was the Rampside model, which, as its name implies, had a large fold-down ramp on the side of the pickup bed. Rampsides were used by the Bell System because of the ease with which cable reels could be rolled in and out of the bed.

The Greenbrier Sportswagon used the same body as the Corvan with window option, but was marketed as a station wagon like the Lakewood, and was available with trim and paint options similar to the cars, arguably making it the first American Minivan.

Continuing from the end of the previous year was the Monza, heavily promoted and sometimes considered "the poor man's Porsche." The Monza was expanded to a four-door as well as a two-door coupe, and garnered around 144,000 sales.

1962 – 1963

The Corvair's innovative flat-6 engine left room for the spare tire, creating even more room in the forward trunk.

In 1962, Chevrolet introduced the 150 hp (112 kW) turbocharged Monza Spyder, making the Corvair one of the first two production automobiles to come with a turbocharger as a factory option, (with the Oldsmobile F-85 Turbo Jetfire of the same year). The Super Deluxe Monza Spyder introduced improved brakes and suspension, and a multi-gauge instrument cluster which included a tachometer, cylinder head temperature gauge and intake manifold pressure gauge. A convertible option was added as well. The 1963 model year saw the end of the Lakewood station wagon and Loadside pickup, and the availability of a long 3.08 gear for improved fuel economy, but the Corvair otherwise remained largely the same as in 1962.

1964

Significant engineering and safety changes occurred in 1964, while the bodies and models available remained the same.

The lineup remained relatively unchanged for the 1964 model year, with the exception of the engine growing from 145 to 164 in³ (2.3 to 2.7 L)due to an increase in stroke; the base power growing from 80 to 95 hp (60 to 70 kW), and the high performance engine growing from 95 to 110 hp (70 to 80 kW). The Spyder engine remained rated at 150 hp (112 kW)despite the displacement increase of the engine. The Rampside pickup was discontinued at the end of the model year.

1964 also saw a critical improvement in the Corvair's suspension; the car's swing axle rear suspension's tendency to lose traction suddenly and without warning when pushed to the limit was tamed by use of an additional transverse leaf spring coupling both rear wheels. The change was insisted upon by new Chevrolet general manager Semon "Bunkie" Knudsen, who according to contemporary John DeLorean had to threaten to resign in order to get the change approved.

However, a young lawyer named Ralph Nader had written a book called Unsafe at Any Speed in which the 1960-63 Corvair (and its purported greater tendency to roll over) was used as a dramatic case study. Even though a 1972 National Highway Traffic Safety Administration safety commission study ultimately exonerated the Corvair and declared it no more unsafe than any similar vehicle of its era, Nader's book, which was published in 1965, dealt a severe blow to sales of the Corvair line. The sporty, inexpensive Ford Mustang, based on the conventionally designed Ford Falcon and introduced in late 1964 in response to the Corvair, ultimately finished off Chevrolet's bold experiment.

1965

Cover of IND 1965 Cars publication, featuring Corvair

A dramatic redesign of the Corvair body and suspension and several powerful new engines came in 1965. The new body style lay somewhere between that of a baby Chevrolet Corvette Stingray and a mid-1960s Italian sports car and foreshadowed the 1967 Chevrolet Camaro that eventually replaced the Corvair. A new fully independent suspension similar to that used on the Corvette replaced the original swing axle rear suspension.

The previous 150 hp (112 kW) Monza Spyder was replaced by the normally-aspirated 140 hp (104 kW) Corsa and the 180 hp (134 kW) Corsa Turbo. The Corsa came with more instruments on the panel and a short throw shifter when equipped with the manual transmission. The standard equipment Corsa 140 horsepower (104 kW) engine was notable for the fact that the engine used 4 single-throat carburetors, larger valves, and dual exhaust — the factory's response to a modification which hot-rodders had been making since the car first appeared; it was available as an option on other Corvair trim levels. The base 95 hp (71 kW) and 110 hp (82 kW) high performance engines were carried forward from 1964 for the 500 and Monza models.

By this point, the more utilitarian station wagon, Panel Van, and pickup body styles had all been dropped in favor of the sportier coupe, hardtop sedan and convertible styles. 1965 would be the last year for the Greenbrier window van, which was retained only because of a few fleet orders, with less than 2000 being built. Chevrolet replaced the Corvair-based vans with the Chevrolet Sportvan/GMC Handi-Van, which used a traditional front engine/rear drive axle borrowed from the Chevy II.

1966 – 1969

The 1966 lineup remained essentially unchanged from 1965, and sales began to decline as a result of Nader's book, the popular (and cheaper) new Mustang, and rumors of the upcoming Camaro. The sales decline was also accelerated by a decision at GM to discontinue further development of the Corvair. One change of note was a more robust 4 speed synchromesh transmission for 1966, using the standard Saginaw gear set used by other GM vehicles. The new transmission was capable of handling more stress, though generally wasn't as smooth shifting as the earlier transmission. Also, the gear ratios were carried over from other GM cars, and were not optimal for a street-driven Corvair. A small flexible plastic air dam was installed below the front apron to alleviate problems with front-end lift at high speeds. It is a popular retrofit to the 1965 models both for functional and aesthetic reasons.

1967 Corvair Monza

In 1967 the Camaro was introduced and the Corvair line was trimmed to the base 500 sedan and coupe, and the Monza sedan, coupe and convertible. The 140 hp (104 kW) and 180 hp (134 kW) engine options were deleted as well, although the 140 HP option would be later reintroduced as a Regular Production Option and would remain available until Corvair production ended.

In 1968 the line was trimmed even further to just the coupe and convertible, and sales were down to 15,400. This model year was the first equipped with true collapsible steering columns, a final response to one of the most valid safety criticisms.

Corvair production finally ceased in 1969 with sales of only 6,000 cars, a victim of Nader's book, Ford's Mustang, and Chevrolet's own Camaro and Nova. Although negative publicity hurt the Corvair, ongoing litigation is believed to have extended the production life of the vehicle, as ending production would have been construed as an admission by General Motors that the product was flawed.

In the 1970s an abortive attempt was made by Corvair tuner John Fitch (driver) to found a company dedicated to acquiring 1965 – 1969 Corvairs in good condition and rebuilding them from the ground up. The finished car was not sold as a restoration, but with newer headlights and taillights and minor mechanical improvements, as a sort of an update. It is not known how many were completed.

Engineering

The Chevrolet Corvair engine, unique for an American car, presented a different set of requirements for mechanics, many of whom treated the engine in the same way as they would an engine of normal design, leading to problems.

An engineering weakness not generally highlighted related to fumes and gases entering the passenger area via the heater system, a problem endemic to an air-cooled engine that uses heat radiated from the engine directly to heat air for the passenger compartment. Carbon monoxide and other noxious or deadly gases could enter the sedan passenger areas if exhaust system gaskets aged or failed using this system, since the gaskets were inside the heater box air intakes and air for engine cooling and passenger heating was mixed together as one common airflow. The 1960 model Corvairs used a GM Harrison division gasoline heater located in the front trunk area, as its standard heater, similar to the Eberspächer heater offered as an auxiliary heater by Volkswagen as a dealer-installed option. It operated independently from fuel in the cars' gas tank, but this feature became optional in 1961 and was dropped in 1965 due to weak consumer demand. Chronic oil leakage from the pushrod tubes, caused by GM's poor choice of pushrod tube seal material, also contaminated the passenger heating air. That air might also become noxious if a 6-inch (152 mm) wide rubber seal almost 16 feet (5 m) long, located between the engine assembly and the body, was not maintained in like-new condition. Another common problem in the earlier years was oil leakage caused by dissimilar metal thermal expansion on the aluminum and steel engine. Chevrolet wrestled with several problems of this nature the entire time the Corvair was in production with varying degrees of success.

The interior air would also be contaminated if the voltage regulator allowed an over-voltage condition and the original battery vent hoses were not attached. The battery, which was mounted in the engine compartment, could emit sulfuric acid vapor if overcharged. Chevrolet installed special battery caps and hoses that vented the battery to air outside the engine compartment, but these were often discarded by owners during the car's life. The Volkswagen Beetle (Type I), another automobile with an air cooled engine, located the battery in the passenger compartment under the rear seat. This may have been a source of noxious interior fumes in that vehicle as well, and was also a fire hazard if the battery terminal insulator was not placed over the battery and someone or something heavy sat on the seat. The Beetle heater system better isolated fresh air from engine cooling air fumes, and was only susceptible to carbon monoxide contamination from the two heat exchanger to muffler seals at the rear of the engine, as opposed to the eight exhaust joints in the Corvair system. The VW Beetle, likewise, was susceptible to poor engine perimeter seal maintenance resulting in contaminated air being sucked into the cooling fan, which supplied passenger compartment heat as in the Corvair.

This air contamination problem is illustrated by the fact that many American cities' taxi regulations had prohibited air-cooled engine cars from being used as taxicabs when they derived their heated air from engine exhaust heat, decades before the Corvair and VW Beetle entered the market.

A criticism in Lawyer Ralph Nader's 1965 book concerned the steering column design. Like most cars of its era, the Corvair's steering column was rigid and could impale the driver in a front-end collision. While the Corvair's steering box was mounted ahead of the front cross-member, it was well behind the frame horns, in what would later be called a "crumple zone," and could, in a severe front-end collision, push the steering column and steering wheel toward the driver. In practice, most driver chest injuries were sustained due to the lack of a shoulder belt, rather than steering column intrusion. Any increase in risk of injury due to steering column intrusion in a front-end collision was, however, more than offset by the absence of an incompressible engine and transmission in the front of the vehicle, which commonly intruded into passenger compartments on vehicles of the era. Chevrolet, aware of Nader's criticism, changed the steering shaft to a two-part design with a frangible joint in the 1966 model year, and a collapsible steering column was provided in 1967, towards the end of the model's life span.

In defense of Nader's criticism of the Corvair's swing axle rear suspension, some writers have pointed to a critical factor in the combination of soft "American-style" springs together with an unusually large and heavy engine for a rear-engine, air-cooled car. Both of these factors would have greatly increased the potential for excessive body lean and over-cambering of the suspension in sharp turns, as compared with smaller and lighter contemporary Volkswagens, Renaults, Porsches, and other rear-engined cars. In addition, the car was designed to avoid terminal oversteer by using very low air pressure in the front tires, typically 12 to 15 pounds force per square inch (80 to 100 kPa), so that they would begin to understeer (slip) before the swing axle oversteer would come into play. Although this pressure was quite adequate for the very lightweight Corvair front end, owners and mechanics, either through ignorance of the necessity for this pressure differential between front and rear or thinking that the pressure was too low for the front, would frequently inflate the front tires to more "normal" pressures, thus ensuring that the rear of the car would lose traction before the front, causing it to oversteer. It should be mentioned that the Corvair is by no means unique in requiring dissimilar front and rear tire pressures for normal controllability. The Ford Explorer had widely-publicized stability problems when equal pressures were used. See Firestone vs Ford Motor Company controversy.

Although Nader probably overstated the severity of the handling problems, as was later found by US National Highway Traffic Safety Administration investigators, Chevrolet made changes to the suspension: in 1964, adding a transverse leaf spring extending between the rear wheels to limit rear wheel camber change. In 1965 the Corvair got a state of the art fully independent rear suspension closely resembling that of the contemporary Corvette, even sharing some components. These changes were, however, viewed as Chevrolet's recognition of possible problems with the original design.

Modifications

Many sports car purists were more interested in the Corvair (particularly the 1965 and later cars) than in more conventional designs, such as the Ford Mustang, despite the latter's power advantage. From the first appearance of the Corvair, a large selection of high-performance equipment and modifications became available for it.

Yenko Stinger

Don Yenko, who had been racing Corvettes, could not compete successfully against the Carroll Shelby Mustangs after they arrived on the scene; he therefore decided to race modified Corvairs, beginning with the 1966 model. As the stock Corvair did not fit into any of the SCCA categories, Yenko had to modify four-carburetor Corsas into "sports cars" by removing the back seat; in the process he would introduce various performance improvements. As the SCCA required 100 cars to be manufactured to homologate the model for production racing, Yenko completed 100 Stingers in one month in 1965. Although all were white, as the SCCA required for American cars at the time, there was a great deal of variety between individual cars; some had exterior modifications including fiberglass engine covers with spoilers, some did not; some received engine upgrades developing 160, 190, 220, or 240 hp (119, 142, 164, or 179 kW). All were equipped by the Chevrolet factory with heavy duty suspension, four speed transmission, quicker steering ratio, positraction differentials (50 with 3.89 gears, and 50 with 3.55 when Chevrolet dropped the 3.89) and dual brake master cylinders (the first application of this by Chevrolet, to become stock equipment the next year). The Stingers competed in Class D Production, which was dominated by the Triumph TR4, which was very quick in racing trim; however in its first race in January 1966, the Stinger was able to come in second by only one second. By the end of the 1966 season, Jerry Thompson had won the Central Division Championship and placed fifth in the 1966 Nationals, Dick Thompson, a highly successful Corvette race driver, had won the Northeast Division Championship, and Jim Spencer had won the Central Division Championship, with Dino Milani taking second place.

The next year, however, Chevrolet dropped the Corsa line, and the Monza line was not initially available stock with the four carburetor engine; the engine was eventually offered as a special performance option, however, along with the 3.89 differential. The Monza instrumentation, however, did not have a tachometer or head temperature gauges, which had to be separately installed. The SCCA, on the other hand, had relaxed its ruling regarding color, and the cars were available in red or blue. It is believed that only fourteen 1967 Stingers were built, but Dana Chevrolet, who distributed Stingers on the US West Coast, ordered an additional three similar cars to be built to Stinger specifications, but with the AIR injection system to meet California emissions laws, with Yenko's permission. A total of 185 Stingers are believed to have been built, the last being YS-9700 built for Goodyear Tire and Rubber Company as a tire test vehicle in 1969 – 1970.

Comedian, television star, and car enthusiast Tim Allen currently owns and races Yenko Stinger #YS-043.

John Fitch Corvair Sprint

Longtime roadracer John Fitch was particularly interested in the Corvair as the basis for a spirited road and track oriented car, due to its handling. The basic Sprint received only minor modifications to the engine, bringing it to 155 horsepower (116 kW), but upgrades to the shock absorbers and springs, adjustments to the wheel alignment, quicker steering ratio, alloy wheels, metallic brake linings, the obligatory wood-rimmed steering wheel (leather available for an additional $9.95) and other such minor alterations made it extremely competitive with European sports cars costing much more. Body options such as spoilers were available, but the most visually remarkable option was the "Ventop", a fiberglass overlay for the C-pillars and rear of the roof that gave the car a "flying buttress" profile.

Fitch went on to design and build a prototype of the Fitch Phoenix, a Corvair-based two-seat sports car, superficially resembling a smaller version of the Mako Shark based Corvette. With a total weight of 1,950 pounds (885 kg), even with a steel body, and with the Corvair engine modified with Weber carburetors to deliver 175 horsepower (130 kW), the car delivered spirited performance for $8,760. Unfortunately, the Traffic Safety Act of 1966 placed restrictions on the ability to produce automobiles on a small scale; this was followed by Chevrolet's decision to terminate production of the Corvair, which confirmed the end of Fitch's plan. He still retains the prototype however, and occasionally exhibits it at car shows.

V8 Corvairs

The ultimate Corvair modification was replacement of the engine with a V8. As daunting as this might seem, two things made it possible:

  1. The Corvair engine rotated in the opposite direction from most other engines, so that if a V8 was placed in the rear seat area (the added weight of a V8 in the original location of the Corvair engine would be abominable to drive), and the transaxle was rotated 180 degrees to meet it, the gearing would drive the car in the proper direction, not four speeds in reverse and one forward
  2. The switch in 1966 to using standard Chevrolet Saginaw gear sets in the manual transmission could handle the torque of a V8.

A radiator occupies the former trunk, in the front of the vehicle. However, the former engine compartment in the rear now is available as luggage space. A complete kit to adapt a Chevrolet small-block V8 to a Corvair was manufactured by a company named Crown Manufacturing, for $600. The resulting vehicle weighed only 2,750 pounds (1250 kg), compared to 3,700 pounds (1680 kg) for a small block Corvette, and possessed independent rear suspension of almost the same design. Crown's prototype with 350 horsepower (261 kW) Corvette engine recorded an elapsed time of 12.22 seconds and 105 miles per hour (169 km/h) in the quarter mile (402 m). An advantage of this modification is that the rearward weight distribution gives excellent traction without the need for slick or "cheater slick" tires, let alone modifying the wheelbase as on the FX cars of the time The mid-engine design also provides optimal handling characteristics. Although a few Corvairs have been modified to accept the Chevrolet big-block engine, the added size of the engine makes the work significantly more difficult, and the result, although a great performer, tends to be unreliable.


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Although a few Corvairs have been modified to accept the Chevrolet big-block engine, the added size of the engine makes the work significantly more difficult, and the result, although a great performer, tends to be unreliable. In addition, diamonds are the subject of various myths and legends. An advantage of this modification is that the rearward weight distribution gives excellent traction without the need for slick or "cheater slick" tires, let alone modifying the wheelbase as on the FX cars of the time The mid-engine design also provides optimal handling characteristics. Clarke's 2061: Odyssey Three (1988) and Neal Stephenson's The Diamond Age (1995). Crown's prototype with 350 horsepower (261 kW) Corvette engine recorded an elapsed time of 12.22 seconds and 105 miles per hour (169 km/h) in the quarter mile (402 m). Notable pieces of fiction include Ian Fleming's Diamonds Are Forever (1956), Arthur C. The resulting vehicle weighed only 2,750 pounds (1250 kg), compared to 3,700 pounds (1680 kg) for a small block Corvette, and possessed independent rear suspension of almost the same design. Diamonds are a common focus of fiction.

A complete kit to adapt a Chevrolet small-block V8 to a Corvair was manufactured by a company named Crown Manufacturing, for $600. The diamond is the birthstone for people born in the month of April, and is also used as the symbol of a sixty-year anniversary, such as a Diamond Jubilee (see hierarchy of precious substances). However, the former engine compartment in the rear now is available as luggage space. However, many people feel very uncomfortable at the thought of wearing the carbonized remains of people as jewelry. A radiator occupies the former trunk, in the front of the vehicle. The LifeGem company further taps modern symbolism by offering to synthetically convert the carbonized remains of people or pets into "memorial diamonds". As daunting as this might seem, two things made it possible:. The Mattachine Society, one of the first and the foremost gay rights groups in the United States, used so-called harlequin diamonds (four smaller diamonds arranged in a pattern to form one larger diamond) as their emblem.

The ultimate Corvair modification was replacement of the engine with a V8. Diamonds were also a symbol of gay community in the 1950s. He still retains the prototype however, and occasionally exhibits it at car shows. Inaccessibility of diamonds to the vast majority of the population limited the popularity of diamonds as betrothal jewels during this period. Unfortunately, the Traffic Safety Act of 1966 placed restrictions on the ability to produce automobiles on a small scale; this was followed by Chevrolet's decision to terminate production of the Corvair, which confirmed the end of Fitch's plan. 1430–40), a pictorial piece depicting a wedding couple. With a total weight of 1,950 pounds (885 kg), even with a steel body, and with the Corvair engine modified with Weber carburetors to deliver 175 horsepower (130 kW), the car delivered spirited performance for $8,760. 1370–80) and the Heftlein brooch of Vienna (ca.

Fitch went on to design and build a prototype of the Fitch Phoenix, a Corvair-based two-seat sports car, superficially resembling a smaller version of the Mako Shark based Corvette. Other early examples of betrothal jewels incorporating diamonds include the Bridal Crown of Blanche (ca. Body options such as spoilers were available, but the most visually remarkable option was the "Ventop", a fiberglass overlay for the C-pillars and rear of the roof that gave the car a "flying buttress" profile. It can be traced to the marriage of Maximilian I (then Archduke of Austria) to Mary of Burgundy in 1477. The basic Sprint received only minor modifications to the engine, bringing it to 155 horsepower (116 kW), but upgrades to the shock absorbers and springs, adjustments to the wheel alignment, quicker steering ratio, alloy wheels, metallic brake linings, the obligatory wood-rimmed steering wheel (leather available for an additional $9.95) and other such minor alterations made it extremely competitive with European sports cars costing much more. The diamond engagement ring is, however, not an original invention of De Beers. Longtime roadracer John Fitch was particularly interested in the Corvair as the basis for a spirited road and track oriented car, due to its handling. The popularity of this modern tradition can be traced directly to the marketing campaigns of De Beers, starting in 1938.

Comedian, television star, and car enthusiast Tim Allen currently owns and races Yenko Stinger #YS-043. Today, diamonds are used to symbolize eternity and love, being often seen adorning engagement rings and sometimes wedding rings as well. A total of 185 Stingers are believed to have been built, the last being YS-9700 built for Goodyear Tire and Rubber Company as a tire test vehicle in 1969 – 1970. In Western culture, diamonds are the traditional emblem of fearlessness and virtue, but have also often associated with power, wealth, crime and misfortune. It is believed that only fourteen 1967 Stingers were built, but Dana Chevrolet, who distributed Stingers on the US West Coast, ordered an additional three similar cars to be built to Stinger specifications, but with the AIR injection system to meet California emissions laws, with Yenko's permission. In Tibetan Buddhism, also known as Vajrayana (Diamond Vehicle), diamonds are an important symbol, and the Diamond Sutra is one of the most popular texts. The SCCA, on the other hand, had relaxed its ruling regarding color, and the cars were available in red or blue. Many long dead cultures have sought to explain diamond's superlative properties through divine or mystical affiliations.

The Monza instrumentation, however, did not have a tachometer or head temperature gauges, which had to be separately installed. It is said the Greeks believed diamonds were tears of the gods; the Romans believed they were splinters of fallen stars. The next year, however, Chevrolet dropped the Corsa line, and the Monza line was not initially available stock with the four carburetor engine; the engine was eventually offered as a special performance option, however, along with the 3.89 differential. The point at which diamonds began to be associated with divinity is not known, but early texts indicate that it was recognized in India since at least 400 BCE. By the end of the 1966 season, Jerry Thompson had won the Central Division Championship and placed fifth in the 1966 Nationals, Dick Thompson, a highly successful Corvette race driver, had won the Northeast Division Championship, and Jim Spencer had won the Central Division Championship, with Dino Milani taking second place. The diamonds themselves were thought to be endowments from the gods and were therefore cherished. The Stingers competed in Class D Production, which was dominated by the Triumph TR4, which was very quick in racing trim; however in its first race in January 1966, the Stinger was able to come in second by only one second. Perhaps the earliest symbolic use of diamonds was as the eyes of Hindu devotional statues.

All were equipped by the Chevrolet factory with heavy duty suspension, four speed transmission, quicker steering ratio, positraction differentials (50 with 3.89 gears, and 50 with 3.55 when Chevrolet dropped the 3.89) and dual brake master cylinders (the first application of this by Chevrolet, to become stock equipment the next year). Because of their extraordinary physical properties, diamonds have been used symbolically since near the time of their first discovery. Although all were white, as the SCCA required for American cars at the time, there was a great deal of variety between individual cars; some had exterior modifications including fiberglass engine covers with spoilers, some did not; some received engine upgrades developing 160, 190, 220, or 240 hp (119, 142, 164, or 179 kW). However, synthetic diamonds may one day be indistinguishable from natural diamonds, and new techniques for simulants (such as coating them with a very thin diamond-like layer of carbon) are making it harder to easily distinguish between simulants and real diamonds. As the SCCA required 100 cars to be manufactured to homologate the model for production racing, Yenko completed 100 Stingers in one month in 1965. The established natural diamond industry has a vested interest in maintaining the distinction between natural diamonds and other diamonds, and has made significant investments toward that end. As the stock Corvair did not fit into any of the SCCA categories, Yenko had to modify four-carburetor Corsas into "sports cars" by removing the back seat; in the process he would introduce various performance improvements. Currently, trained gemologists with appropriate equipment are able to distinguish natural diamonds from all synthetic and simulant diamonds, and identify all enhanced natural diamonds.

Don Yenko, who had been racing Corvettes, could not compete successfully against the Carroll Shelby Mustangs after they arrived on the scene; he therefore decided to race modified Corvairs, beginning with the 1966 model. These include laser drilling to remove inclusions, application of sealants to fill cracks, treatments to improve a white diamond's color grade, and treatments to give fancy color to a white diamond. From the first appearance of the Corvair, a large selection of high-performance equipment and modifications became available for it. Diamond enhancements are specific treatments, performed on natural diamonds (usually those already cut and polished into a gem), which are designed to better the gemological characteristics of the stone in one or more ways. Many sports car purists were more interested in the Corvair (particularly the 1965 and later cars) than in more conventional designs, such as the Ford Mustang, despite the latter's power advantage. Both CZ and moissanite are synthetically produced for use as a diamond simulant. These changes were, however, viewed as Chevrolet's recognition of possible problems with the original design. The most familiar diamond simulant to most consumers is cubic zirconia (commonly abbreviated as CZ); recently moissanite has also gained cachet as a popular diamond simulant.

In 1965 the Corvair got a state of the art fully independent rear suspension closely resembling that of the contemporary Corvette, even sharing some components. Materials which have similar gemological characteristics to diamond but are not real mined or synthetic diamond are known as diamond simulants. Although Nader probably overstated the severity of the handling problems, as was later found by US National Highway Traffic Safety Administration investigators, Chevrolet made changes to the suspension: in 1964, adding a transverse leaf spring extending between the rear wheels to limit rear wheel camber change. A diamond's gem quality, which is not as dependent on material properties as industrial applications, has invited both imitation and the invention of procedures to enhance the gemological properties of natural diamonds. See Firestone vs Ford Motor Company controversy. Diamonds have been manufactured synthetically for over fifty years. The Ford Explorer had widely-publicized stability problems when equal pressures were used. This process has historically produced industrial-grade diamonds, but synthetic diamond producers have recently begun to penetrate the gem diamond market.

It should be mentioned that the Corvair is by no means unique in requiring dissimilar front and rear tire pressures for normal controllability. A portion of this demand is now being met by synthetic diamonds, man-made diamonds which have similar properties to natural diamonds. Although this pressure was quite adequate for the very lightweight Corvair front end, owners and mechanics, either through ignorance of the necessity for this pressure differential between front and rear or thinking that the pressure was too low for the front, would frequently inflate the front tires to more "normal" pressures, thus ensuring that the rear of the car would lose traction before the front, causing it to oversteer. The gemological and industrial uses of diamond have created a large demand for raw stones. In addition, the car was designed to avoid terminal oversteer by using very low air pressure in the front tires, typically 12 to 15 pounds force per square inch (80 to 100 kPa), so that they would begin to understeer (slip) before the swing axle oversteer would come into play. [4]. Both of these factors would have greatly increased the potential for excessive body lean and over-cambering of the suspension in sharp turns, as compared with smaller and lighter contemporary Volkswagens, Renaults, Porsches, and other rear-engined cars. According to the Rio Tinto Group, in 2002 the diamonds produced and released to the market were valued at US$9 billion as rough diamonds, US$14 billion after being cut and polished, US$28 billion in wholesale diamond jewelry, and retail sales of US$57 billion.

In defense of Nader's criticism of the Corvair's swing axle rear suspension, some writers have pointed to a critical factor in the combination of soft "American-style" springs together with an unusually large and heavy engine for a rear-engine, air-cooled car. Diamonds can be sold already set in jewelry, or as is increasingly popular, sold unset ("loose"). Chevrolet, aware of Nader's criticism, changed the steering shaft to a two-part design with a frangible joint in the 1966 model year, and a collapsible steering column was provided in 1967, towards the end of the model's life span. This is the final tightly controlled step in the diamond supply chain; wholesalers and even retailers are able to buy relatively small lots of diamonds at the bourses, after which they are prepared for final sale to the consumer. Any increase in risk of injury due to steering column intrusion in a front-end collision was, however, more than offset by the absence of an incompressible engine and transmission in the front of the vehicle, which commonly intruded into passenger compartments on vehicles of the era. There are 24 registered diamond bourses. In practice, most driver chest injuries were sustained due to the lack of a shoulder belt, rather than steering column intrusion. Diamonds which have been prepared as gemstones are sold on diamond exchanges called bourses.

While the Corvair's steering box was mounted ahead of the front cross-member, it was well behind the frame horns, in what would later be called a "crumple zone," and could, in a severe front-end collision, push the steering column and steering wheel toward the driver. The recent expansion of this industry in India, employing low cost labor, has allowed smaller diamonds to be prepared as gems than was previously economically feasible. Like most cars of its era, the Corvair's steering column was rigid and could impale the driver in a front-end collision. Demonstrating this, India produces 90% of all cut and polished diamonds by number, but only 55% by value. A criticism in Lawyer Ralph Nader's 1965 book concerned the steering column design. Cutting centers with lower costs of labor, notably Surat in Gujarat, India, handle a larger number of smaller carat diamonds, while smaller quantities of larger or more valuable diamonds are more likely to be handled in Europe or North America. This air contamination problem is illustrated by the fact that many American cities' taxi regulations had prohibited air-cooled engine cars from being used as taxicabs when they derived their heated air from engine exhaust heat, decades before the Corvair and VW Beetle entered the market. Recently, diamond cutting centers have been established in China, India, and Thailand.

The VW Beetle, likewise, was susceptible to poor engine perimeter seal maintenance resulting in contaminated air being sucked into the cooling fan, which supplied passenger compartment heat as in the Corvair. Traditional diamond cutting centers are Antwerp, Amsterdam, Johannesburg, New York, and Tel Aviv. The Beetle heater system better isolated fresh air from engine cooling air fumes, and was only susceptible to carbon monoxide contamination from the two heat exchanger to muffler seals at the rear of the engine, as opposed to the eight exhaust joints in the Corvair system. The cutting and polishing of rough diamonds is a specialized skill that is concentrated in a limited number of locations worldwide. This may have been a source of noxious interior fumes in that vehicle as well, and was also a fire hazard if the battery terminal insulator was not placed over the battery and someone or something heavy sat on the seat. Once purchased by sightholders, diamonds are cut and polished in preparation for sale as gemstones. The Volkswagen Beetle (Type I), another automobile with an air cooled engine, located the battery in the passenger compartment under the rear seat. DTC performs sophisticated sorting of rough diamonds into over 16,000 categories, and then sells bulk lots of rough diamonds to a limited number of sightholders a few times a year.

Chevrolet installed special battery caps and hoses that vented the battery to air outside the engine compartment, but these were often discarded by owners during the car's life. The Diamond Trading Company, or DTC, is a subsidiary of De Beers and markets rough diamonds produced both by De Beers mines and other mines from which it purchases rough diamond production; in whole, about two thirds of all rough diamonds pass through the company. The battery, which was mounted in the engine compartment, could emit sulfuric acid vapor if overcharged. In 2003, this constituted total production of nearly US$9 billion in value. The interior air would also be contaminated if the voltage regulator allowed an over-voltage condition and the original battery vent hoses were not attached. Currently, gem production totals nearly 30 million carats (6,000 kg) of cut and polished stones annually, and over 100 million carats (20,000 kg) of diamonds are sold for industrial use each year. Chevrolet wrestled with several problems of this nature the entire time the Corvair was in production with varying degrees of success. Although the Kimberly Process has been somewhat successful in limiting the number of conflict diamonds entering the market, conflict diamonds smuggled to market continue to persist to some degree.

Another common problem in the earlier years was oil leakage caused by dissimilar metal thermal expansion on the aluminum and steel engine. The Kimberley Process provides documentation and certification of diamond exports from producing countries to ensure that the proceeds of sale are not being used to fund criminal or revolutionary activities. That air might also become noxious if a 6-inch (152 mm) wide rubber seal almost 16 feet (5 m) long, located between the engine assembly and the body, was not maintained in like-new condition. In response to public concerns that their diamond purchases were contributing to war and human rights abuses in central Africa and west Africa, the diamond industry and diamond-trading nations introduced the Kimberley Process in 2002, which is aimed at ensuring that conflict diamonds do not become intermixed with the diamonds not controlled by such rebel groups. Chronic oil leakage from the pushrod tubes, caused by GM's poor choice of pushrod tube seal material, also contaminated the passenger heating air. Diamonds sold through this process are known as conflict diamonds or blood diamonds. It operated independently from fuel in the cars' gas tank, but this feature became optional in 1961 and was dropped in 1965 due to weak consumer demand. In some of the more politically unstable central African and west African countries, revolutionary groups have taken control of diamond mines, using proceeds from diamond sales to finance their operations.

The 1960 model Corvairs used a GM Harrison division gasoline heater located in the front trunk area, as its standard heater, similar to the Eberspächer heater offered as an auxiliary heater by Volkswagen as a dealer-installed option. Diamond prospectors continue to search the globe for diamond-bearing kimberlite and lamproite pipes. Carbon monoxide and other noxious or deadly gases could enter the sedan passenger areas if exhaust system gaskets aged or failed using this system, since the gaskets were inside the heater box air intakes and air for engine cooling and passenger heating was mixed together as one common airflow. There are also commercial deposits being actively mined in the Northwest Territories of Canada, Siberia (mostly in Yakutia territory, for example Mir pipe and Udachnaya pipe), Brazil, and in Northern and Western Australia. An engineering weakness not generally highlighted related to fumes and gases entering the passenger area via the heater system, a problem endemic to an air-cooled engine that uses heat radiated from the engine directly to heat air for the passenger compartment. Today, most commercially viable diamond deposits are in Africa, notably in South Africa, Namibia, Botswana, the Republic of the Congo, Angola and Sierra Leone. The Chevrolet Corvair engine, unique for an American car, presented a different set of requirements for mechanics, many of whom treated the engine in the same way as they would an engine of normal design, leading to problems. The first non-Indian diamond source was found in Brazil in 1725.

It is not known how many were completed. Historically diamonds were known to be found only in alluvial deposits in southern India; India led the world in diamond production from the time of their discovery in approximately the 9th century BCE to the mid-18th century CE, but the commercial potential of these sources has been exhausted. The finished car was not sold as a restoration, but with newer headlights and taillights and minor mechanical improvements, as a sort of an update. The concentration of power only loosens at the retail level, where diamonds are sold by a limited number of distributors, known as sightholders, to jewelers around the world. In the 1970s an abortive attempt was made by Corvair tuner John Fitch (driver) to found a company dedicated to acquiring 1965 – 1969 Corvairs in good condition and rebuilding them from the ground up. In fact, the amount of power which De Beers has consolidated historically prevented it from direct trade with the United States, as its trade practices led to an indictment for violating antitrust regulations (the case was settled in 2004). Although negative publicity hurt the Corvair, ongoing litigation is believed to have extended the production life of the vehicle, as ending production would have been construed as an admission by General Motors that the product was flawed. The diamond supply chain is controlled by a limited number of powerful businesses, and is also highly concentrated in a small number of locations around the world.

Corvair production finally ceased in 1969 with sales of only 6,000 cars, a victim of Nader's book, Ford's Mustang, and Chevrolet's own Camaro and Nova. See also: List of diamond mines. This model year was the first equipped with true collapsible steering columns, a final response to one of the most valid safety criticisms. Significant research efforts in Japan, Europe, and the United States are under way to capitalize on the potential offered by diamond's unique material properties, combined with increased quality and quantity of supply starting to become available from synthetic diamond manufacturers. In 1968 the line was trimmed even further to just the coupe and convertible, and sales were down to 15,400. Garnering much excitement is the possible use of diamond as a semiconductor suitable to build microchips from, or the use of diamond as a heat sink in electronics. The 140 hp (104 kW) and 180 hp (134 kW) engine options were deleted as well, although the 140 HP option would be later reintroduced as a Regular Production Option and would remain available until Corvair production ended. With the continuing advances being made in the production of synthetic diamond, future applications are beginning to become feasible.

In 1967 the Camaro was introduced and the Corvair line was trimmed to the base 500 sedan and coupe, and the Monza sedan, coupe and convertible. Specialized applications include use in laboratories as containment for high pressure experiments (see diamond anvil), high-performance bearings, and limited use in specialized windows. It is a popular retrofit to the 1965 models both for functional and aesthetic reasons. Diamonds are embedded in drill tips or saw blades, or ground into a powder for use in grinding and polishing applications. A small flexible plastic air dam was installed below the front apron to alleviate problems with front-end lift at high speeds. Most uses of diamonds in these technologies do not require large diamonds; in fact, most diamonds that are gem-quality except for their small size, can find an industrial use. Also, the gear ratios were carried over from other GM cars, and were not optimal for a street-driven Corvair. The dominant industrial use of diamond is in cutting, drilling, grinding, and polishing.

The new transmission was capable of handling more stress, though generally wasn't as smooth shifting as the earlier transmission. In addition to mined diamonds, synthetic diamonds found industrial applications almost immediately after their invention in the 1950s; another 400 million carats (80,000 kg) of synthetic diamonds are produced annually for industrial use—nearly four times the mass of natural diamonds mined over the same period. One change of note was a more robust 4 speed synchromesh transmission for 1966, using the standard Saginaw gear set used by other GM vehicles. This helps explain why 80% of mined diamonds (equal to about 100 million carats or 20,000 kg annually), unsuitable for use as gemstones and known as bort, are destined for industrial use. The sales decline was also accelerated by a decision at GM to discontinue further development of the Corvair. Industrial diamonds are valued mostly for their hardness and heat conductivity, making many of the gemological characteristics of diamond, including clarity and color, mostly irrelevant. The 1966 lineup remained essentially unchanged from 1965, and sales began to decline as a result of Nader's book, the popular (and cheaper) new Mustang, and rumors of the upcoming Camaro. The market for industrial-grade diamonds operates much differently from its gem-grade counterpart.

Chevrolet replaced the Corvair-based vans with the Chevrolet Sportvan/GMC Handi-Van, which used a traditional front engine/rear drive axle borrowed from the Chevy II. This coordinated campaign has lasted decades and continues today; it is perhaps best captured by the now-familiar slogan "a diamond is forever". 1965 would be the last year for the Greenbrier window van, which was retained only because of a few fleet orders, with less than 2000 being built. Ayer's multifaceted marketing campaign included product placement, advertising the diamond itself rather than the De Beers brand, and building associations with celebrities and royalty. By this point, the more utilitarian station wagon, Panel Van, and pickup body styles had all been dropped in favor of the sportier coupe, hardtop sedan and convertible styles. N.W. The base 95 hp (71 kW) and 110 hp (82 kW) high performance engines were carried forward from 1964 for the 500 and Monza models. Ayer & Son, the advertising firm retained by De Beers in the mid-20th century, succeeded in reviving the American diamond market and opened up new markets, even in countries where no diamond tradition had existed before.

The standard equipment Corsa 140 horsepower (104 kW) engine was notable for the fact that the engine used 4 single-throat carburetors, larger valves, and dual exhaust — the factory's response to a modification which hot-rodders had been making since the car first appeared; it was available as an option on other Corvair trim levels. N.W. The Corsa came with more instruments on the panel and a short throw shifter when equipped with the manual transmission. The De Beers diamond advertising campaign is acknowledged as one of the most successful and innovative ones in history. The previous 150 hp (112 kW) Monza Spyder was replaced by the normally-aspirated 140 hp (104 kW) Corsa and the 180 hp (134 kW) Corsa Turbo. De Beers has used its monopoly position to establish strict price controls, and aggressively market diamonds directly to consumers in world markets. A new fully independent suspension similar to that used on the Corvette replaced the original swing axle rear suspension. At one time it was thought over 80 percent of the world's rough diamonds passed through the Diamond Trading Company (DTC, a subsidiary of De Beers) in London, but presently the figure is estimated at around 60 percent.

The new body style lay somewhere between that of a baby Chevrolet Corvette Stingray and a mid-1960s Italian sports car and foreshadowed the 1967 Chevrolet Camaro that eventually replaced the Corvair. The company and its subsidiaries own mines that produce some 40 percent of annual world diamond production, and control distribution channels handling nearly two thirds of all gem diamonds. A dramatic redesign of the Corvair body and suspension and several powerful new engines came in 1965. De Beers owns or controls a significant portion of the world's rough diamond production facilities (mines) and distribution channels for gem-quality diamonds. The sporty, inexpensive Ford Mustang, based on the conventionally designed Ford Falcon and introduced in late 1964 in response to the Corvair, ultimately finished off Chevrolet's bold experiment. The De Beers company holds a clearly dominant position in the industry, and has done so since soon after its founding in 1888. Even though a 1972 National Highway Traffic Safety Administration safety commission study ultimately exonerated the Corvair and declared it no more unsafe than any similar vehicle of its era, Nader's book, which was published in 1965, dealt a severe blow to sales of the Corvair line. The production and distribution of diamonds is largely consolidated in the hands of a few key players, and concentrated in traditional diamond trading centers (the most important being Antwerp).

However, a young lawyer named Ralph Nader had written a book called Unsafe at Any Speed in which the 1960-63 Corvair (and its purported greater tendency to roll over) was used as a dramatic case study. They are based in Johannesburg, South Africa and London, England. The change was insisted upon by new Chevrolet general manager Semon "Bunkie" Knudsen, who according to contemporary John DeLorean had to threaten to resign in order to get the change approved. One hallmark of the trade in gem-quality diamonds is its remarkable concentration: wholesale trade and diamond cutting is limited to a few locations (most importantly New York, Antwerp, London, Tel Aviv, Amsterdam and Surat), and a single company—De Beers—controls over half of all trade in diamonds. 1964 also saw a critical improvement in the Corvair's suspension; the car's swing axle rear suspension's tendency to lose traction suddenly and without warning when pushed to the limit was tamed by use of an additional transverse leaf spring coupling both rear wheels. Unlike precious metals such as gold or platinum, gem diamonds do not trade as a commodity: there is a substantial mark-up in the sale of diamonds, and there is not a very active market for resale of diamonds. The Rampside pickup was discontinued at the end of the model year. A large trade in gem-grade diamonds exists.

The Spyder engine remained rated at 150 hp (112 kW)despite the displacement increase of the engine. While a large trade in both types of diamonds exists, the two markets act in dramatically different ways. The lineup remained relatively unchanged for the 1964 model year, with the exception of the engine growing from 145 to 164 in³ (2.3 to 2.7 L)due to an increase in stroke; the base power growing from 80 to 95 hp (60 to 70 kW), and the high performance engine growing from 95 to 110 hp (70 to 80 kW). The diamond industry can be broadly separated into two basically distinct categories: one dealing with gem-grade diamonds and another for industrial-grade diamonds. Significant engineering and safety changes occurred in 1964, while the bodies and models available remained the same. The largest flawless and colorless (grade D) diamond is the Millennium Star (1990) at 203.04 carats. The 1963 model year saw the end of the Lakewood station wagon and Loadside pickup, and the availability of a long 3.08 gear for improved fuel economy, but the Corvair otherwise remained largely the same as in 1962. One of the diamonds cut from it, Cullinan I or the Great Star of Africa, was formerly the largest cut diamond at 530.2 carats, but now that title has been taken by the Golden Jubilee (1985), a 545.67 carat yellow-brown diamond.

A convertible option was added as well. The Cullinan Diamond, owned by Queen Elizabeth II was the largest gem-quality rough diamond ever found (1905), at 3,106.75 carats. The Super Deluxe Monza Spyder introduced improved brakes and suspension, and a multi-gauge instrument cluster which included a tachometer, cylinder head temperature gauge and intake manifold pressure gauge. A number of large diamonds have become historically significant objects, as their inclusion in various sets of crown jewels and the purchase, sale, and sometimes theft of notable diamonds, have sometimes become politicized. In 1962, Chevrolet introduced the 150 hp (112 kW) turbocharged Monza Spyder, making the Corvair one of the first two production automobiles to come with a turbocharger as a factory option, (with the Oldsmobile F-85 Turbo Jetfire of the same year). Popularity continued to rise as new cuts were developed that enhanced the diamond's aesthetic appeal, and has largely continued unabated to this day; diamonds have proven popular with all classes in society as their cost has become within reach. Continuing from the end of the previous year was the Monza, heavily promoted and sometimes considered "the poor man's Porsche." The Monza was expanded to a four-door as well as a two-door coupe, and garnered around 144,000 sales. However, within a century diamonds were popular gems among the moneyed aristocratic and merchant classes, and by at latest 1477 had begun to be used in wedding rings.

The Greenbrier Sportswagon used the same body as the Corvan with window option, but was marketed as a station wagon like the Lakewood, and was available with trim and paint options similar to the cars, arguably making it the first American Minivan. In the 13th century, King Louis IX of France established a law that only the king could own diamonds. Rampsides were used by the Bell System because of the ease with which cable reels could be rolled in and out of the bed. The rise in popularity of diamonds as gems seems to have paralleled increasing availability through European history. The Loadside was a fairly typical pickup of the era, except for the rear engine, forward controls, and a strange pit in the middle of the bed, The more popular pickup was the Rampside model, which, as its name implies, had a large fold-down ramp on the side of the pickup bed. In 1919, Marcel Tolkowsky developed an ideal round brilliant cut design that has set the standard for comparison of modern gems; however, diamond cuts have continued to be refined. There were also two models of pickup available. Over the following centuries, various diamond cuts were introduced which increasingly demonstrated the fire and brilliance that makes diamonds treasured today: the table cut, the briolette (around 1476), the rose cut (mid-16th century), and by the mid-17th century, the Mazarin, the first brilliant cut diamond design.

The Corvan model was available in a myriad of configurations as both a panel van and a window van. By 1375, a guild of diamond polishers had been established at Nuremberg. That same year, Chevrolet also introduced the Corvair 95 line of light-duty truck, which used the Corvair driveline and were forward-control, with the driver sitting over the front wheels, as in the Volkswagen Type 2. During this time, the taboo against cutting diamonds into gem shapes, which was established over 1,000 years earlier in the traditions of India, ended allowing the development of diamond cutting technology to begin in earnest. Engine heat and gasoline odors migrating up through the floor of the station wagon proved to be a persistent problem, and the wagon was relatively short-lived. Around 1300, the flow of diamonds into Europe increased via Venice's trade network, with most flowing through the low country ports of Bruges, Antwerp, and Amsterdam. A station wagon, the Lakewood, was also added to the lineup in 1961, and it contained a total of 68 ft³ (1.9 m³) of cargo room — 58 in the main passenger compartment, and another 10 in the "trunk" under the hood. Until the late Middle Ages, diamonds were most prized in their natural octahedral state, perhaps with the crystal surfaces polished to increase luster and remove foreign material.

The gasoline heater remained an option through 1964. In Europe, however, diamonds disappeared for almost 1,000 years following the rise of Christianity because of two effects: early Christians rejected diamonds because of their earlier use in amulets, and Arabic traders restricted the flow of trade between Europe and India. The standard heater was changed from the gasoline heater to engine cooling air ducted into the passenger compartment. Archeological evidence from Yemen suggests that diamonds were used as drill tips as early as the 4th century BCE. The high-performance engine was rated at 98 hp (73 kW). In China, diamonds seem to have been used primarily for engraving jade and drilling holes in beads. The base engine was still rated at 80 hp (60 kW) when paired with the manual transmissions and 84 hp (63 kW) when mated to the optional automatic transmission. The Roman writer Pliny the Elder noted diamond's ornamental uses, as well as its usefulness to engravers because of its hardness, in his work Naturalis Historia.

The Corvair engine received its first size increase to 145 in³, courtesy of a slight increase in bore size. Diamonds were traded to both the east and west of India and were recognized by various cultures for their gemological or industrial uses. For 1961 Chevrolet added an optional four-speed manual transmission to augment the standard three-speed manual and optional two-speed automatic. At that scale, the surface of the modern diamond-polished corundum closely resembled that of the axes; however, the polishes of the latter were superior. Despite its late introduction, the Monza sold 12,000 copies, making it one of the most popular Corvairs. Although there are diamond deposits now known to exist close to the burial sites, no direct evidence of coeval diamond mining has been found: the researchers came to this conclusion by polishing corundum using various lapidary abrasives and modern techniques then comparing the results using an atomic force microscope. Optional was a more powerful engine rated at 95 horsepower, thanks to a more radical camshaft and low-restriction exhaust. team of archaeologists reported the discovery of four corundum-rich stone ceremonial burial axes originating from China's Liangzhu and Sanxingcun cultures (4000 BCE–2500 BCE) which, because of the axes' specular surfaces, the scientists believe were polished using diamond powder [2] [3].

The line quickly grew from plain, four-door sedans with bench seats (the base 500 and slightly more upscale 700) to the Monza 900, a two-door coupe with bucket seats and plush trim introduced late in the model year. In February 2005, a joint Chinese-U.S. Passenger compartment heat was supplied by a gasoline heater mounted in the luggage compartment. Ownership was restricted among various castes by color, with only kings being allowed to own all colors of diamond. A novel feature available for two-doors was a fold-down rear seat, included on some higher-level models. Diamonds quickly became associated with divinity, being used to decorate religious icons, and were believed to bring good fortune to those who carried them. The early 1960 models were conceived as economy cars, and had boxy styling, basic trim, and few amenities to keep prices down despite the relatively expensive and unique powertrain. The earliest written reference can be found in the Sanskrit text Arthasastra, which was completed around 296 BCE, describes diamond's hardness, luster, and dispersion.

The design was championed by Ed Cole, Chevrolet chief engineer in the early 1950s and general manager in the late 1950s, as an answer to the growing popularity of small, lightweight imported cars. Diamonds are thought to have been first recognized and mined in India, where significant alluvial deposits of the stone could then be found. The Corvair name originated as a fastback show car in 1954, which, like many Chevy concept cars of the period, were based on the Corvette, including the Chevrolet Nomad and Chevrolet Impala. However, cleanliness might reflect a diamond's sentimental value: some jewelers have noted a correlation between ring cleanliness and marriage quality [1]. . Cleanliness does not affect the diamond's market value, as any competent jeweler will clean the diamond before offering it for sale. Doing so in Southern California and being caught by the Los Angeles Police Department was a guaranteed ticket to a weekend in jail. Some jewelers provide their customers with ammonia-based cleaning kits; ultrasonic cleaners are also popular.

The first Corvairs (1960 – 1964) were factory equipped with an ignition lock wherein it was possible to start the car and then remove the key. Maintaining a clean diamond can sometimes be difficult, as jewelry settings can obstruct cleaning efforts, and oils, grease, and other hydrophobic materials adhere well to a diamond's surface. For 24 hours, the Corvair was tested at the Riverside International Raceway in Riverside, California, one car did a roll but the other did the 24 hour drive and only lost a quart (1 L) of oil (Source: Riverside Raceway Palace of Speed by Dick Wallen). Current practice is to thoroughly clean a diamond before grading its color. The first engines produced as little as 80 hp (60 kW), but later developed as much as 180 hp (134 kW). Historically, some jewelers' stones were misgraded because of smudges on the girdle, or dye on the culet. The entire line (which eventually grew to incorporate sedans, coupes, convertibles, vans, pickups and station wagons) initially shared an aluminum, air-cooled 140 in³ (2.3 L) flat-6 engine. Colored dye or smudges can affect the perceived color of a diamond.

The "trunk", on the other hand, was in the front of the vehicle, while the spare tire was stored above the flat engine, saving trunk space. Even a thin film absorbs some light that could have been reflected to the person looking at the diamond. It was a rear-engined vehicle in the style of the Volkswagen Beetle and the Porsche 356 Speedster. Water, dirt, or grease on the bottom of a diamond interferes with the diamond's brilliance and fire. The Corvair was part of GM's innovative A-body line of cars, but this was by far the most unusual, due to the location and design of its engine. Dirt or grease on the top of a diamond reduces its luster. The Corvair — like the Ford Falcon, Studebaker Lark, Rambler, and the Plymouth Valiant — was created in response to the small, sporty and fuel-efficient automobiles being imported from Europe by Volkswagen, Renault and others. A clean diamond is more brilliant and fiery than the same diamond when it is "dirty".

Design began in 1956 under the auspices of Ed Cole, and the first vehicles rolled off the assembly line in late 1959 as part of the 1960 model year (in which it was named Motor Trend magazine's Car of the Year). Although it is not one of the four Cs, cleanliness affects a diamond's beauty as much as any of the four Cs. The Corvair remains one of GMs most unusual creations. Since the per carat price of diamond shifts around key milestones (such as 1.00 carat), many one-carat diamonds are the result of compromising "Cut" for "Carat." Some jewelry experts advise consumers to buy a 0.99 carat diamond for its better price or buy a 1.10 carat diamond for its better cut, avoiding a 1.00 carat diamond which is more likely to be a poorly cut stone. The Corvair was offered in a wide range of body styles (such as a four-door sedan, coupe, convertible, station wagon, pickup, panel van, a window van called the Greenbrier) and featured an air-cooled engine, which was unusual for American cars at the time. Sometimes the cutters compromise and accept lesser proportions and symmetry in order to avoid inclusions or to preserve the carat rating. The Chevrolet Corvair was a rear-engined automobile produced by General Motors from 1960 to 1969. Even with modern techniques, the cutting and polishing of a diamond crystal always results in a dramatic loss of weight; rarely is it less than 50%.

The switch in 1966 to using standard Chevrolet Saginaw gear sets in the manual transmission could handle the torque of a V8. Oddly shaped crystals such as macles are more likely to be cut in a fancy cut—that is, a cut other than the round brilliant—which the particular crystal shape lends itself to. The Corvair engine rotated in the opposite direction from most other engines, so that if a V8 was placed in the rear seat area (the added weight of a V8 in the original location of the Corvair engine would be abominable to drive), and the transaxle was rotated 180 degrees to meet it, the gearing would drive the car in the proper direction, not four speeds in reverse and one forward. The round brilliant cut is preferred when the crystal is an octahedron, as often two stones may be cut from one such crystal. The choice of cut is often decided by the original shape of the rough stone, location of the inclusions and flaws to be eliminated, the preservation of the weight, popularity of certain shapes amongst consumers and many other considerations. The process of shaping a rough diamond into a polished gemstone is both an art and a science.

EightStar Diamond has results of the FireScope. Hearts on Fire Diamond has results of the Hearts and Arrows viewer. Solasfera Diamond has results of Hearts and Arrows viewer, GemEx BrillianceScope, and FireScope. Along with this shift there are a few companies that provide results on these viewers and machines in addition to the original 4c's.

These viewers and machines often help consumers determine the light preformance results of the diamond in addition the the traditional 4 C's. SymmetriScope or IdealScope (tests for light leakage, light return and proportions), Hearts and Arrows Viewer (test for "hearts and arrows" characteristic pattern observable on stones exhibiting high symmetry), GemEx BrillianceScope (tests for direct light performance results of a diamond), Isee2 Machine (tests for diffused light performance results of a diamond), and ASET (test for AGS cut grade). They included the FireScope, a.k.a. A number of specially modified viewers and machines have been developed toward this end.

Recently, there has been a shift away from grading cut by the use of various angles and proportions toward measuring the performance of a cut stone. Several different theories on the "ideal" proportions of a diamond have been and continue to be advocated by professional gemologists. An inferior cut will produce a stone that appears dark at the center and in some extreme cases the ring settings may show through the top of the diamond as shadows. A well executed round brilliant cut should reflect most light out from the tabletop and make the diamond appear white when viewed from the top.

For a round brilliant cut, there is a balance between "brilliance" and "fire." When a diamond is cut for too much "fire," it looks like a cubic zirconia, which gives off much more "fire" than real diamond. A poorly cut diamond with facets cut only a few degrees out of alignment can result in a poorly performing stone. A number of factors, including proportion, symmetry, and the relative angles of various facets, are determined by the quality of the cut and can affect the performance of a diamond. In addition to carrying the most importance to a diamond's quality as a gemstone, the cut is also the most difficult to quantitatively judge.

The skill with which a diamond is cut determines its ability to reflect and refract light. The quality of a diamond's cut is widely considered the most important of the four Cs in determining the beauty of a diamond; indeed, it is commonly acknowledged that a well-cut diamond can appear to be of greater carat weight, and have clarity and color appear to be of better grade than they actually are. These newly developed cuts are viewed by many as more of an attempt at brand differentiation by diamond sellers, than actual improvements to the state of the art. Some of these include extra facets.

The past decades have seen the development of new diamond cuts, often based on a modification of an existing cut. The princess cut is also popular amongst diamond cutters: of all the cuts, it wastes the least of the original crystal. Cuts are influenced heavily by fashion: the baguette cut—which accentuates a diamond's luster and downplays its fire—was all the rage during the Art Deco period, whereas the princess cut—which accentuates a diamond's fire rather than its luster—is currently gaining popularity. Generally speaking, these "fancy cuts" are not held to the same strict standards as Tolkowsky-derived round brilliants and there are less specific mathematical guidelines of angles which determine a well-cut stone.

Diamonds which are not cut to the specifications of Tolkowsky's round brilliant shape (or subsequent variations) are known as "fancy cuts." Popular fancy cuts include the baguette (from the French, resembling a loaf of bread), marquise, princess (square outline), heart, briolette (a form of the rose cut), and pear cuts. Diamonds are cut into a variety of shapes that are generally designed to accentuate these features. Diamonds do not show all of their beauty as rough stones; instead, they must be cut and polished to exhibit the characteristic fire and brilliance that diamond gemstones are known for. Mathematically, the diameter in millimeters of a round brilliant should approximately equal 6.5 times the cube root of carat weight, or 11.1 times the cube root of gram weight.

Typically a round brilliant 1.0 carat diamond should have a diameter of about 6.5 mm. Another quick indication is the overall diameter. "Ideal" round brilliant diamonds should not have a depth percentage greater than 62.5%. The depth percentage is the overall quickest indication of the quality of the cut of a round brilliant.

So a poorly cut 1.0 carat diamond may have the same diameter and appear as large as a 0.85 carat diamond. Neither of the these tactics make the diamond appear any bigger, but it also greatly reduces the sparkle of the diamond. There is a financial premium for a diamond that weighs the magical 1.0 carat, so often the girdle is made thicker or the depth is increased. However, there is a small range in which the diamond can be considered "ideal." Today, because of the relative importance of carat weight in society, many diamonds are often intentionally cut poorly to increase carat weight.

The further the diamond's characteristics are from Tolkowsky's ideal, the less light will be reflected. A normal girdle should be about 1%–2% of the overall diameter. However, a thin girdle is required in reality in order to prevent the diamond from easily chipping in the setting. Tolkowsky's ideal dimensions did not include a girdle.

This should be a negligible diameter, otherwise light leaks out of the bottom. The culet is the tiny point at the bottom of the diamond. Tolkowsky defines the ideal dimensions to have:. The function of the crown is to diffuse light into various colors and the pavilion's function to reflect light back through the top of the diamond.

The girdle is the thin unpolished middle. The modern round brilliant has 57 facets (polished faces), counting 33 on the crown (the top half), and 24 on the pavilion (the lower half). He developed the round brilliant cut by calculating the ideal shape to return and scatter light when a diamond is viewed from above. The techniques for cutting diamonds have been developed over hundreds of years, with perhaps the greatest achievements made in 1919 by mathematician and gem enthusiast Marcel Tolkowsky.

Round brilliant diamonds, the most common, are guided by these specific guidelines, though fancy cut stones are not able to be as accurately guided by mathematical specifics. There are mathematical guidelines for the angles and length ratios at which the diamond is supposed to cut at in order to reflect the maximum amount of light. Often diamond cut is confused with "shape.". The cut of a diamond describes the quality of workmanship and the angles to which a diamond is cut.

The cut of a diamond describes the manner in which a diamond has been shaped and polished from its beginning form as a rough stone to its final gem proportions. Diamond cutting is the art and science of creating a gem-quality diamond out of mined rough. Gemologists have developed rating systems for fancy colored diamonds, but they are not in common use because of the relative rarity of colored diamonds. Intense yellow coloration is considered one of the fancy colors, and is separate from the color grades of white diamonds.

Diamonds with unusual or intense coloration are sometimes labeled "fancy" by the diamond industry. A variety of impurities and structural imperfections cause different colors in diamonds, including yellow, pink, blue, red, green, brown, and other hues. While even a pale pink or blue hue may increase the value of a diamond, more intense coloration is usually considered more desirable and commands the highest prices. In contrast to yellow or brown hues, diamonds of other colors are much rarer and more valuable.

N-Y are usually appear light yellow or brown. Diamonds graded D-F are considered "colorless", G-J are considered "near-colorless", K-M are "slightly colored". Oddly enough, diamonds graded Z are also rare, and the bright yellow color is also highly valued. Diamonds with higher color grades are rarer, in higher demand, and therefore more expensive, than lower color grades.

The system uses a benchmark set of either natural diamonds of known color grade, or precision-crafted cubic zirconia; test lighting conditions are also standardized and carefully controlled. The GIA has developed a rating system for color in white diamonds, from "D" to "Z" (with D being "colorless" and Z having a bright yellow coloration), which has been widely adopted in the industry and is universally recognized, superseding several older systems once used in different countries. This effect is present in almost all white diamonds; in only the rarest diamonds is the coloration due to this effect undetectable. The most common impurity, nitrogen, replaces a small proportion of carbon atoms in a diamond's structure and causes a yellowish to brownish tint.

Most diamonds used as gemstones are basically transparent with little tint, or white diamonds. For example, most white diamonds are discounted in price as more yellow hue is detectable, while intense pink or blue diamonds (such as the Hope Diamond) can be dramatically more valuable. Depending on the hue and intensity of a diamond's coloration, a diamond's color can either detract from or enhance its value. The color of a diamond may be affected by chemical impurities and/or structural defects in the crystal lattice.

However, in reality almost no gem-sized natural diamonds are absolutely perfect. A chemically pure and structurally perfect diamond is perfectly transparent with no hue, or color. (see the main article for more detail). Diamonds are graded by the major societies on a scale ranging from Flawless to Imperfect.

Large cracks close to or breaking the surface may reduce a diamond's resistance to fracture. However, large clouds can affect a diamond's ability to transmit and scatter light. Most inclusions present in gem-quality diamonds do not affect the diamonds' performance or structural integrity. Those that do not have a visible inclusion are known as "eye-clean" and are preferred by most buyers, although visible inclusions can sometimes be hidden under the setting in a piece of jewelry.

Of that top 20 percent, a significant portion contains an inclusion or inclusions that are visible to the naked eye upon close inspection. Only about 20 percent of all diamonds mined have a clarity rating high enough for the diamond to be considered appropriate for use as a gemstone; the other 80 percent are relegated to industrial use. Diamonds become increasingly rare when considering higher clarity gradings. The Gemological Institute of America (GIA) and others have developed systems to grade clarity, which are generally based on those inclusions which are visible to a trained professional when a diamond is viewed from above, under 10x magnification.

The number, size, color, relative location, orientation, and visibility of inclusions can all affect the relative clarity of a diamond. Inclusions may be crystals of a foreign material or another diamond crystal, or structural imperfections such as tiny cracks that can appear whitish or cloudy. Clarity is a measure of internal defects of a diamond called inclusions. is also widely used for diamond necklaces, bracelets and other similar jewelry pieces.

T.c.w. when placed for sale, indicating the mass of the diamonds in both earrings and not each individual diamond. Diamond solitaire earrings, for example, are usually quoted in t.c.w. Total carat weight (t.c.w.) is a phrase used to describe the total mass of diamonds or other gemstone in a piece of jewelry, when more than one gemstone is used.

Because of this, diamond prices (particularly among wholesalers and other industry professionals) are often quoted per carat, rather than per stone. For example, a buyer may place an order for 100 carats of 0.5 carat, D–F, VS2-SI1, excellent cut diamonds, indicating he wishes to purchase 200 diamonds (100 carats total mass) of those approximate characteristics. In the wholesale trade of gem diamonds, carat is often used in denominating lots of diamonds for sale. Jewelers often trade diamonds at negotiated discounts off the Rapaport price (e.g., "R -3%").

A weekly price list published by Rapaport of New York, of diamond prices per carat, for different diamond cuts, clarity and weights, is currently considered the de-facto retail price baseline. As an example, a 0.95 carat diamond may have a significantly lower price per carat than a comparable 1.05 carat diamond, because of differences in demand. Instead, there are sharp jumps around milestone carat weights, as demand is much higher for diamonds weighing just more than a milestone than for those weighing just less. The price per carat does not increase smoothly with increasing size.

A review of comparable diamonds available for purchase in September 2005 demonstrates this effect (approximate prices for round cut, G color, VS2 diamonds with "1A" cut grade, as listed on http://www.pricescope.com):. All else being equal, the value of a diamond increases exponentially in relation to carat weight, since larger diamonds are both rarer and more desirable for use as gemstones. The point unit—equal to one one-hundredth of a carat (0.01 carat, or 2 mg)—is commonly used for diamonds of less than one carat. One carat is defined as exactly 200 milligrams (about 0.007 ounce).

The carat weight measures the mass of a diamond. While carat weight and cut angles are mathematically defined, the clarity and color are judged by the trained human eye and are therefore open to slight variance in interpretation. There are four major gemological associations which "certify" diamonds: that is, define the four Cs of a diamond. Cleanliness also dramatically affects a diamond's beauty.

These characteristics include physical characteristics such as the presence of fluorescence, as well as data on a diamond's history including its source and which gemological institute performed evaluation services on the diamond. Other characteristics not described by the four Cs can and do influence the value or appearance of a gem diamond. Consumers who purchase individual diamonds are often advised to use the four Cs to pick the diamond that is "right" for them; to these is sometimes added the "fifth C" of cost. More detailed information from within each characteristic can then be used to determine actual market value for individual stones.

Most gem diamonds are traded on the wholesale market based on single values for each of the four Cs; for example knowing that a diamond is rated as 1.5 carats, VS2 clarity, F color, excellent cut, is enough to reasonably establish an expected price range. Four characteristics, known informally as the four Cs, are now commonly used as the basic descriptors of diamonds: these are carat, clarity, color, and cut. Over time, especially since around 1900, experts in the field of gemology have developed methods of characterizing diamonds and other gemstones based on the characteristics most important to their value as a gem. The dispersion of white light into a rainbow of colors, known in the trade as fire, is the other primary characteristic of gem diamonds, and has been highly prized throughout history.

The use of diamonds as gemstones of decorative value is the most familiar use to most people today, and is also the earliest use, with decorative use of diamonds stretching back into antiquity. Diamonds can also be brought to the surface through certain processes which may occur when two continental plates collide forcefully, although this phenomenon is less understood and currently assumed to be uncommon. Diamonds have also rarely been found in deposits left behind by glaciers (notably in Wisconsin and Indiana); however, in contrast to alluvial deposits, glacial deposits are not known to be of significant concentration and are therefore not viable commercial sources of diamond. These include alluvial deposits and deposits along existing and ancient shorelines, where loose diamonds tend to accumulate because of their approximate size and density.

Secondary sources of diamonds include all areas where a significant number of diamonds, eroded out of their kimberlite or lamproite matrix, accumulate because of water or weather action. A volcanic pipe containing diamonds is known as a primary source of diamonds. Once diamonds have been forced to the surface by magma in a volcanic pipe, they may erode out and be distributed over a large area. Kimberlite deposits are known as blue ground for the deeper serpentinized part of the deposits, or as yellow ground for the near surface smectite clay and carbonate weathered and oxidized portion.

The most common indicator minerals are chromian garnets (usually bright red Cr-pyrope, and occasionally green ugrandite-series garnets), eclogitic garnets, orange Ti-pyrope, red high chromian spinels, dark chromite, bright green Cr-diopside, glassy green olivine, black picroilmenite, and magnetite. These minerals are rich in chromium (Cr) or titanium (Ti), elements which impart bright colors to the minerals. Certain indicator minerals typically occur within diamondiferous kimberlites and are used as mineralogic tracers in the search for diamond deposits by prospectors. These rocks are characteristically rich in magnesium bearing olivine, pyroxene, and amphibole minerals which are usually altered to serpentine under near surface conditions.

The magma itself does not contain diamond; instead, it acts as an elevator that carries deep-formed rocks and material upward. The magma in such volcanic pipes is usually one of two characteristic types, which cool into igneous rock known as either kimberlite or lamproite. Diamond-bearing volcanic pipes are most commonly found in the oldest regions of continental crust, which relates to the fact that these areas are the coolest portions of the earth's crust, and therefore diamonds can form at the shallowest depths. Below these typically small surface volcanic craters are formations known as volcanic pipes, which contain material that was pushed toward the surface of the earth by volcanic action, but did not erupt before the volcanic activity ceased.

The magma for such a volcano must originate at a depth where diamonds can be formed, 90 miles (150 km) deep or more (three times or more the depth of source magma for most volcanoes); this is a relatively rare occurrence. Diamond-bearing rock is forced close to the surface through deep-origin volcanic eruptions. Microdiamonds are now used as one indicator of ancient meteorite impact sites. Very small diamonds, known as microdiamonds or nanodiamonds, have been found in impact craters where meteors strike the Earth and create shock zones of high pressure and temperature where diamond formation can occur.

Diamonds can also form in other natural high-pressure, high-temperature events. Diamonds (especially those from secondary deposits) are commonly found coated in nyf, an opaque gum-like skin. This is all due to the conditions in which they form. Sometimes they are found grown together or form double "twinned" crystals grown together at the surfaces of the octahedron.

The crystals can have rounded off and unexpressive edges and can be elongated. As diamond's crystal structure has a cubic arrangement of the atoms, they have many facets that belong to a cube, octahedron, rhombicosidodecahedron, tetrakis hexahedron or disdyakis dodecahedron. Diamonds occur most often as euhedral or rounded octahedra and twinned octahedra known as macles. Diamonds that have come to the Earth's surface are generally very old, ranging from under 1 billion to 3.3 billion years old.

These two different source carbons have measurably different 13C:12C ratios. In contrast, eclogitic diamonds contain organic carbon from organic detritus that has been pushed down from the surface of the Earth's crust through subduction (see plate tectonics) before transforming into diamond. Some diamonds, known as harzburgitic, are formed from inorganic carbon originally found deep in the Earth's mantle. Through studies of carbon isotope ratios (similar to the methodology used in carbon dating) except using the stable isotopes C-12 and C-13, it has been shown that the carbon found in diamonds comes from both inorganic and organic sources.

Long periods of exposure to these high pressures and temperatures allow diamond crystals to grow larger. Diamond formation under oceanic crust takes place at greater depths because of higher temperatures, which require higher pressure for diamond formation. Under continental crust, diamonds form starting at depths of about 150 kilometers (90 miles), where pressure is roughly 5 gigapascals and the temperature is around 1200 degrees Celsius (2200 degrees Fahrenheit). On Earth, the formation of diamonds is possible because there are regions deep within the Earth that are at a high enough pressure and temperature that the formation of diamonds is thermodynamically favorable (see the diamond phase diagram and geotherms here).

Diamond is formed by prolonged exposure of carbon bearing materials to high pressure and temperature.
. Because diamond has such high thermal conductance it is already used in semiconductor manufacture to prevent silicon and other semiconducting materials from overheating. Specially purified synthetic diamond has the highest thermal conductivity (2000–2500 W/(m·K), five times more than copper) of any known solid at room temperature.

Most natural blue diamonds contain boron atoms which replace carbon atoms in the crystal matrix, and also have high thermal conductivity. Unlike most electrical insulators, diamond is a good conductor of heat because of the strong covalent bonding within the crystal. Blue diamonds which are not boron-doped, such as those recently recovered from the Argyle diamond mine in Australia that owe their color to an overabundance of hydrogen atoms, are not semiconductors. Blue diamonds owe their semiconductive property to boron impurities, which act as a doping agent and cause p-type semiconductor behavior.

Except for most blue diamonds, which are semiconductors, diamonds are good electrical insulators. Most diamonds show no fluorescence although colored diamonds show a wider range of fluorescence than the blue fluorescence normally observed in clear diamonds. Nearly all diamonds fluoresce bluish-white, yellow or green under X-rays and this property is used extensively in mining to separate the fluorescing diamond from the non-fluorescing rock. Some diamonds exhibit fluorescence of various colors (predominately blue) under long wave ultraviolet light.

This is owed to their high refractive index of 2.417 (at 589.3 nm), which causes total internal reflection to occur. The luster of a diamond, a characterization of how light interacts with the surface of a crystal, is brilliant and is described as adamantine, which simply means diamond-like. This strong ability to split white light into its component colors is an important aspect of diamond's attraction as a gemstone, giving it impressive prismatic action that results in so-called fire in a well-cut stone. Diamonds exhibit a high dispersion of visible light.

However, owing to a very large kinetic energy barrier, diamonds are metastable; under normal conditions, it would take an extremely long time (possibly more than the age of the Universe) for diamond to decay into graphite. This was shown in the late 18th century, and previously described during Roman times. Diamonds will burn at approximately 800 degrees Celsius, providing that enough oxygen is available. At surface air pressure (one atmosphere), diamonds are not as stable as graphite, and so the decay of diamond is thermodynamically favorable (ΔG = −2.99 kJ / mol).

The most common impurity, nitrogen, causes a yellowish or brownish tinge. Most diamond impurities replace a carbon atom in the crystal lattice. Colored diamonds contain impurities or structural defects that cause the coloration, while pure or nearly pure diamonds are transparent and colorless. Diamonds with a detectable hue to them are known as colored diamonds.

Diamonds occur in a variety of transparent hues — colorless, white, steel, blue, yellow, orange, red, green, pink, brown—or colored black. Diamonds cut into certain particular shapes are therefore more prone to breakage than others. As with any material, the macroscopic geometry of a diamond contributes to its resistance to breakage. Toughness relates to a material's ability to resist breakage from forceful impact.

Unlike hardness, which only denotes resistance to scratching, diamond's toughness is only fair to good. Unlike many other gems, it is well-suited to daily wear because of its resistance to scratching—perhaps contributing to its popularity as the preferred gem in an engagement ring or wedding ring, which are often worn every day. Because it can only be scratched by other diamonds, it maintains its polish extremely well, keeping its luster over long periods of time. The hardness of diamonds also contributes to its suitability as a gemstone.

Industrial applications, especially as drill bits and engraving tools, also date to ancient times. Industrial-grade diamonds are either unsuitable for use as gems or synthetically produced, which lowers their price and makes their use economically feasible. Other specialized applications also exist or are being developed, including use as semiconductors: some blue diamonds are natural semiconductors, in contrast to most other diamonds, which are excellent electrical insulators. Common industrial adaptations of this ability include diamond-tipped drill bits and saws, or use of diamond powder as an abrasive.

As the hardest known naturally occurring material, diamond can be used to polish, cut, or wear away any material, including other diamonds. It is one of the most known and most useful of more than 3,000 known minerals. Industrial use of diamonds has historically been associated with their hardness; this property makes diamond the ideal material for cutting and grinding tools. 1990).

Most other diamonds show more evidence of multiple growth stages, which produce inclusions, flaws and defect planes in the crystal lattice all of which affect their hardness (Taylor et al. Their hardness is considered to be a product of the crystal growth form, which is single stage growth crystal. These diamonds are generally small, perfect to semiperfect octahedra and are used to polish other diamonds. The hardest diamonds in the world are diamonds from the New England area in New South Wales, Australia.

However, aggregated diamond nanorods, an allotrope of carbon first synthesized in 2005, are now believed to be even harder than diamond. Diamond's hardness has been known since antiquity, and is the source of its name. Diamond is the hardest known naturally occurring material, scoring 10 on the relative Mohs scale of mineral hardness and having an absolute hardness value of between 167 and 231 gigapascals in various tests. A colorless, grey or black diamond with a tiny radial structure is a spherulite.

A cryptocrystalline variety of diamond is called carbonado. Lonsdaleite is a polymorph of diamond (and a distinct mineral species) that crystallizes with hexagonal symmetry; it is rarely found in nature, but is characteristic of synthetic diamonds. Other elements of the carbon group such as silicon have forms analogous to diamond. Graphite, another allotrope of carbon, has a rhombohedral crystal structure and as a result shows dramatically different physical characteristics — contrary to diamond, graphite is a very soft, dark grey, opaque mineral.

The tetrahedral arrangement of atoms in a diamond crystal is the source of many of diamond's properties. The unit cell of diamond has a two atom basis at (0,0,0) and (1/4,1/4,1/4), which means half of the atoms are at lattice points and the other half are offset by (1/4,1/4,1/4), where 1 is the length of a side of the unit cell. Diamonds typically crystallize in the face-centered cubic crystal system and consist of tetrahedrally bonded carbon atoms. These properties form the basis for most modern applications of diamond.

Most notable among these properties are the extreme hardness of diamond, its high dispersion index, and high thermal conductivity. Humans have been able to adapt diamonds for many uses because of the material's exceptional physical characteristics. Diamond is a transparent crystal of pure carbon consisting of tetrahedrally bonded carbon atoms. See also: Crystallographic defects in diamond.

.
. There are also allegations that the De Beers Group misuses its dominance in the industry to control supply and manipulate price via monopolistic practices. The mining and distribution of natural diamonds are subjects of frequent controversy—such as with concerns over the sale of conflict diamonds by African paramilitary groups.

They are generally mined from volcanic pipes, which are deep in the Earth where the high pressure and temperature enables the formation of the crystals. Most natural diamonds originate from central and southern Africa, although significant sources of the mineral have been discovered in Canada, Russia, Brazil, and Australia. Although nearly four times the mass of natural diamonds are produced as synthetic diamond each year, the vast majority of synthetic diamond production remains small, imperfect diamonds suitable only for industrial-grade use, with gem-quality synthetic diamonds only recently becoming available. Popularity of diamonds has risen since the 19th century because of improved cutting and polishing techniques, and they are commonly judged by the "four Cs": carat, clarity, color, and cut.

They have been treasured as gems since their use as religious icons in India at least 2,500 years ago—and usage in drill bits and engraving tools also dates to early human history. The name "diamond" derives from the ancient Greek adamas (αδάμας; "impossible to tame"). About 130 million carats (26,000 kg) are mined annually, with a total value of nearly USD $9 billion. Diamonds are specifically renowned as a mineral with superlative physical qualities - they make excellent abrasives because they can only be scratched by other diamonds, which also means they hold a polish extremely well and retain luster.

Diamond is one of the two best known forms (or allotropes) of carbon, whose hardness and high dispersion of light make it useful for industrial applications and jewelry (the other equally well known allotrope is graphite). Crown Depth (Depth of crown divided by crown diameter) = 16.2%. Pavilion Depth (Depth of pavilion divided by overall diameter) = 43.1%. Crown Angle (Angle between the girdle and the crown) = 34.5°.

Pavilion Angle (Angle between the girdle and the pavilion) = 40.75°. Depth percentage (Overall depth divided by the overall diameter) = 59.3%. Table percentage (table diameter divided by overall diameter) = 53%. European Gemological Laboratory (EGI) has a similar reputation to the IGL.

International Gemological Laboratory (IGL) is a generally respected laboratory but suffers from a negative industry reputation for its grading practices, which are perceived by critics as being either less conservative or less consistent than the GIA and AGS. American Gemological Society (AGS) is not as widely recognized nor as old as the GIA, but garners an equally high reputation. Gemological Institute of America (GIA) was the first laboratory to issue modern diamond reports, and holds the highest reputation amongst gemologists for its consistent, conservative grading.

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