This article is about the mineral or gemstone, for other uses see: Topaz (disambiguation).Topaz 4 Carat Oval Shape Topaz Gemstone Ring Enhanced with Azotic(r)Treatment Heart Cut Sky Blue Topaz Ring
The mineral topaz is a silicate of aluminium and fluorine with the chemical formula Al2SiO4(F,OH)2. It crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces, the basal pinacoid often being present. It has an easy and perfect basal cleavage and so gemstones or other fine specimens should be handled with care to avoid developing cleavage flaws. The fracture is conchoidal to uneven. Topaz has a hardness of 8, a specific gravity of 3.4-3.6, and a vitreous lustre. Pure topaz is transparent but is usually tinted by impurities; typical topaz is wine or straw-yellow. They may also be white, gray, green, blue, or reddish-yellow and transparent or translucent. When heated, yellow topaz often becomes reddish-pink. It can also be irradiated, turning the stone a light and distinctive shade of blue. A recent trend in jewelry is the manufacture of topaz specimens that display iridescent colors, by applying a thin layer of titanium oxide via physical vapor deposition.
Topaz is found associated with the more acid rocks of the granite and rhyolite type and may be found with fluorite and cassiterite. It can be found in the Ural and Ilmen mountains, Czech Republic, Saxony, Norway, Sweden, Japan, Brazil, Mexico, and the United States.
Etymology and historical/mythical usage
The name "topaz" is derived from the Greek topazos, "to seek," which was the name of an island in the Red Sea that was difficult to find and from which a yellow stone (now believed to be a yellowish olivine) was mined in ancient times. In the Middle Ages the name topaz was used to refer to any yellow gemstone, but now the name is only properly applied to the silicate described above.
According to Rebbenu Bachya, the word "Leshem" in the verse Exodus 28:19 means "Topaz" and was the stone on the Ephod representing the tribe of Dan.
Topaz is also the birthstone of November.Example of Heat Treated Topaz-Pink Topaz Pear Cut Ring
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Topaz is also the birthstone of November. After use, turquoise should be gently cleaned with a soft cloth to avoid a build up of residue, and should be stored in its own box to avoid scratching by harder gems. According to Rebbenu Bachya, the word "Leshem" in the verse Exodus 28:19 means "Topaz" and was the stone on the Ephod representing the tribe of Dan. Care should therefore be taken when wearing such jewels: cosmetics, including sunscreen and hairspray, should be applied before putting on turquoise jewellery, and they should not be worn to a beach or other sun-bathed environment. In the Middle Ages the name topaz was used to refer to any yellow gemstone, but now the name is only properly applied to the silicate described above. Prolonged exposure to direct sunlight may also discolour or dehydrate turquoise. The name "topaz" is derived from the Greek topazos, "to seek," which was the name of an island in the Red Sea that was difficult to find and from which a yellow stone (now believed to be a yellowish olivine) was mined in ancient times. Being a phosphate mineral, turquoise is inherently fragile and sensitive to solvents; perfume and other cosmetics will attack the finish and may alter the colour of turquoise gems, as will skin oils.
It can be found in the Ural and Ilmen mountains, Czech Republic, Saxony, Norway, Sweden, Japan, Brazil, Mexico, and the United States. Bonded and "reconstituted" material is worth considerably less. Topaz is found associated with the more acid rocks of the granite and rhyolite type and may be found with fluorite and cassiterite. All other factors being equal, untreated turquoise will always command a higher price. A recent trend in jewelry is the manufacture of topaz specimens that display iridescent colors, by applying a thin layer of titanium oxide via physical vapor deposition. Controversy exists as to whether some of these treatments should be acceptable, but one can be more or less forgiven universally: This is the light waxing or oiling applied to most gem turquoise to improve its colour and lustre; if the material is of high quality to begin with, very little of the wax or oil is absorbed and the turquoise therefore does not "rely" on this impermanent treatment for its beauty. It can also be irradiated, turning the stone a light and distinctive shade of blue. Turquoise is treated in many different ways, some more permanent and radical than others.
When heated, yellow topaz often becomes reddish-pink. Like coral and other opaque gems, turquoise is commonly sold at a price according to its physical size in millimetres rather than carat weight. They may also be white, gray, green, blue, or reddish-yellow and transparent or translucent. Calibrated stones—that is, stones adhering to standard jewellery setting measurements—may also be more sought after. Pure topaz is transparent but is usually tinted by impurities; typical topaz is wine or straw-yellow. Uniformity of colour is desired, and in finished pieces the quality of workmanship is also a factor; this includes the quality of the polish and the symmetry of the stone. Topaz has a hardness of 8, a specific gravity of 3.4-3.6, and a vitreous lustre. Such material is sometimes described as "spiderweb matrix"; it is most valued in the Southwest United States and Far East, but is not highly appreciated in the Near East where unblemished and vein-free material is ideal (regardless of how complimentary the veining may be).
The fracture is conchoidal to uneven. The mother rock or matrix in which turquoise is found can often be seen as splotches or a network of brown or black veins running through the stone in a netted pattern; this veining may add value to the stone if the result is complimentary, but such a result is uncommon. It has an easy and perfect basal cleavage and so gemstones or other fine specimens should be handled with care to avoid developing cleavage flaws. Whatever the colour, turquoise should not be excessively soft or chalky; even if treated, such lesser material (to which most turquoise belongs) is liable to fade or discolour over time and will not hold up to normal use in jewellery. It crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces, the basal pinacoid often being present. In Tibet, however, a greener blue is said to be preferred. The mineral topaz is a silicate of aluminium and fluorine with the chemical formula Al2SiO4(F,OH)2. Richness of colour is the chief determiner of value in turquoise; generally speaking, the most desirable is a strong sky to "robin's egg" blue (in reference to the eggs of the American Robin); value decreases with the increase of green hue, lightening of colour, and mottling.
This article is about the mineral or gemstone, for other uses see: Topaz (disambiguation).. For example, the use of a heated probe applied to an inconspicuous spot will reveal oil, wax, or plastic treatment with certainty. Mineral galleries. As is so often with gems, full disclosure is frequently not given; it is therefore left to gemmologists to detect these treatments in suspect stones, using a variety of testing methods—some of which are necessarily destructive. Mindat with location data. Doublets, like the aforementioned treatments, are legal provided they are disclosed to the customer before sale. Webmineral. Some turquoise is cut with the mother rock serving as a base; these are usually not considered doublets but may have an intrinsic value lower than that of "whole" stones.
These are termed doublets and can be very deceptive in certain jewellery setting styles (such as closed back and bevel settings). As the finer turquoise is often found as thin seams, it may be glued to a base of stronger foreign material as a means of reinforcement. This process claims to use only medium grade material at a minimum, leaving the turquoise harder and with a better colour and lustre. Zachery.
Another treatment—the details of which remain undisclosed—is the so-called Zachery process, named after its developer, electrical engineer and turquoise trader James E. Much (if not all) of this "reconstituted" material is likely a complete fabrication (with no natural components), or may have foreign filler material added to it (see Imitations section). Perhaps the most radical of treatments is "reconstitution", wherein supposedly fragments of fine material too small to be used singly are powdered and then bonded to form a solid mass. Dyes have also been used to darken the veins of turquoise.
(With some skill, oil and wax treatments can be restored.) Likewise, the use of Prussian blue and other dyes—often in conjunction with bonding treatments—to enhance (that is, make uniform or completely change) colour is regarded as fraudulent by purists—especially since some dyes may fade or rub off on the wearer. Oiled and waxed stones are also prone to "sweating" under even gentle heat or if exposed to too much sun, and they may develop a white surface film or bloom over time. The majority of American material is now treated in this manner; although it is a costly process requiring many months to complete, without impregnation most American mining operations would be unprofitable. The epoxy binding technique was first developed in the 1950s and has been attributed to Colbaugh Processing of Arizona, a company that still operates today.
Plastic and water glass are technologically superior to oil and wax in that the former treatment are far more permanent and stable, and can be applied to material too friable for oil or wax to be of sufficient help; such material is termed "bonded" or "stabilized" turquoise. Conversely, the later development of pressure impregnation of otherwise unsaleable chalky American material by epoxy and plastics (such as polystyrene) and water glass—also producing a wetting effect in addition to improving durability—are rejected by some as too radical an alteration. Historically, light waxing and oiling were the first treatments to be used (since ancient times), providing a wetting effect (thereby enhancing the colour and lustre); this treatment is more or less acceptable by tradition, and because such material is usually of a higher grade to begin with. Turquoise is treated to enhance both its colour and durability (i.e., increased hardness and decreased porosity).
Even material used in authentic Native American and Tibetan jewellery is often fake or, at best, heavily treated. Imitation turquoise is so prevalent that it likely outnumbers real turquoise by a wide margin. Differences in specific gravity, refractive index, light absorption (as evident in a material's absorption spectrum), and other physical and optical properties are also considered as means of separation. Some destructive tests may, however, be necessary; for example, the application of diluted hydrochloric acid will cause the carbonates odontolite and magnesite to effervesce and howlite to turn green, while a heated probe may give rise to the acrid smell so indicative of plastic.
Staining between grain boundaries may be visible in dyed imitations. Glass and plastic will have a much greater translucency, with bubbles or flow lines often visible just below the surface. These fakes are detected by gemmologists using a number of tests, relying primarily on non-destructive, close examination of surface structure under magnification; a featureless, pale blue background peppered by flecks or spots of whitish material is the typical surface appearance of natural turquoise, while manufactured imitations will appear radically different in both colour (usually a uniform dark blue) and texture (usually granular or sugary). While rarely encountered today, odontolite was once mined in large quantities—specifically for its use as a substitute for turquoise—in southern France.
Other natural materials occasionally confused with or used in lieu of turquoise include: variscite; faustite; chrysocolla (especially when impregnating quartz); lazulite; smithsonite; hemimorphite; wardite; and a fossil bone or tooth called odontolite or "bone turquoise", coloured blue naturally by the mineral vivianite. Dyed chalcedony, jasper, and marble is less common, and much less convincing. The most common imitation of turquoise encountered today is dyed howlite and magnesite, both white in their natural states, and the former also having natural (and convincing) black veining similar to that of turquoise. Gilson turquoise is made in both a uniform colour and with black "spiderweb matrix" veining not unlike the natural Nevada material.
Most of these products differ markedly from natural turquoise in both physical and chemical properties, but in 1972 Pierre Gilson introduced one fairly close to a true synthetic (it does differ in chemical composition owing to a binder used, meaning it is best described as a simulant rather than a synthetic). Later glass and enamel were also used, and in modern times more sophisticated ceramics, porcelain, plastics, and various assembled, pressed, bonded, and sintered products (composed of various copper and aluminium compounds) have been developed: examples of the latter include "Viennese turquoise", made from precipitated aluminium phosphate coloured by copper oleate; and "neolith", a mixture of bayerite and copper phosphate. The Egyptians were apparently the first to produce an artificial imitation of turquoise, in the glazed earthenware product faience. Scholars also disagree as to which tribes each stone is meant to represent.
Of the four stones in the third row, the first and second have been translated to be turquoise by various scholars; others disagree, however, translating the stones to be jacinth (zircon) and agate respectively . Attached to the ephod, the breastplate was adorned with twelve gemstones set in gold and arranged in four rows, each stone engraved with the name of one of the Twelve Tribes of Israel. Turquoise may have significance in Judeo-Christian scripture: In the Book of Exodus, the construction of a "breastplate of judgment" is described as part of the priestly vestments of Aaron (Exodus 28:15–30). In Western culture, turquoise is also the traditional birthstone for those born in the month of December.
While strong sky blues remain superior in value, mottled green and yellowish material is popular with artisans. Lesser material may be carved into fetishes, such as those crafted by the Zuni. In contemporary Western use, turquoise is most often encountered cut en cabochon in silver rings, bracelets, often in the Native American style, or as tumbled or roughly hewn beads in chunky necklaces. 1810, was a staple of Egyptian Revival pieces.
Turquoise, already favoured for its pastel shades since c. These excavations, including that of Tutankhamun's tomb, created great public interest in the western world, subsequently influencing jewellery, architecture, and art of the time. The French conducted archaeological excavations of Egypt from the mid-19th-century through the early 20th. (A similar blue ceramic has been recovered from Bronze Age burial sites in the British Isles.).
Turquoise, associated with the goddess Hathor, was so liked by the Ancient Egyptians that it became (arguably) the first gemstone to be imitated, the fair semblance created by an artificial glazed ceramic product known as faience. Set in gold, the gem was fashioned into beads, used as inlay, and often carved in a scarab motif, accompanied by carnelian, lapis lazuli, and in later pieces, coloured glass. It also adorned rings and great sweeping necklaces called pectorals. The Egyptian use of turquoise stretches back as far as the First Dynasty and possibly earlier; however, probably the most well-known pieces incorporating the gem are those recovered from Tutankhamun's tomb, most notably the Pharaoh's iconic burial mask which was liberally inlaid with the stone.
Most of the pieces made today, with turquoise usually roughly polished into irregular cabochons set simply in silver, are meant for inexpensive export to Western markets and are probably not accurate representations of the original style. Cabochons of imported turquoise, along with coral, was (and still is) used extensively in the silver and gold jewellery of Tibet and Mongolia, where a greener hue is said to be preferred. Persian turquoise was often engraved with devotional words in Arabic script which was then inlaid with gold. The Persian style and use of turquoise was later brought to India following the establishment of the Mughal Empire there, its influence seen in high purity gold jewellery (together with ruby and diamond) and in such buildings as the Taj Mahal.
In Persia, turquoise was the de facto national stone for millennia, extensively used to decorate objects (from turbans to bridles), mosques, and other important buildings both inside and out, such as the Medresseh-I Shah Husein Mosque of Isfahan. The distinctive silver jewellery produced by the Navajo and other Southwestern Native American tribes today is a rather modern development, thought to date from circa 1880 as a result of European influences. The Ancestral Puebloans (Anasazi) of the Chaco Canyon and surrounding region are believed to have prospered greatly from their production and trading of turquoise objects. Among these peoples turquoise was used in mosaic inlay, in sculptural works, and was fashioned into toroidal beads and freeform pendants.
Like the Aztecs, the Pueblo, Navajo and Apache tribes cherished turquoise for its amuletic use; the latter tribe believe the stone to afford the archer dead aim. Natural resins, bitumen and wax were used to bond the turquoise to the objects' base material; this was usually wood, but bone and shell were also used. The Aztecs inlaid turquoise, together with gold, quartz, malachite, jet, jade, coral, and shells, into provocative (and presumably ceremonial) mosaic objects such as masks (some with a human skull as their base), knives, and shields. A common belief shared by many of these civilizations held that turquoise possessed certain prophylactic qualities; it was thought to change colour with the wearer's health and protect him or her from untoward forces.
It was apparently unknown in India until the Muhgal period, and unknown in Japan until the 18th century. Despite being one of the oldest gems, probably first introduced to Europe (through Turkey) with other Silk Road novelties, turquoise did not become important as an ornamental stone in the West until the 14th century, following a decline in the Catholic Church's influence which allowed the use of turquoise in secular jewellery. The pastel shades of turquoise have endeared it to many great cultures of antiquity: it has adorned the rulers of Ancient Egypt, the Aztecs (and possibly other Pre-Columbian Mesoamericans), Persia, Mesopotamia, the Indus Valley, and to some extent in ancient China since at least the Shang Dynasty . Other notable localities include: Afghanistan; Australia (Victoria and Queensland); northern Chile (Chuquicamata); Cornwall; Saxony; Silesia; and Turkestan.
However, the existence of these deposits is doubted by some due to a lack of corroboration. In Tibet, where green turquoise has long been appreciated, gem-quality deposits purportedly exist in the mountains of Derge and Nagari-Khorsum in the east and west of the region respectively. Most Chinese material is exported, but a few carvings worked in a manner similar to jade exist. Additionally, Marco Polo reported turquoise found in present-day Sichuan.
Gem-quality material, in the form of compact nodules, is found in the fractured, silicified limestone of Yunxian and Zhushan, Hubei province. China has been a minor source of turquoise for 3,000 years or more. These treatments include innocuous waxing and more controversial procedures, such as dyeing and impregnation (see Treatments). In an attempt to recoup profits and meet demand, most American turquoise is treated or enhanced to a certain degree.
Until the 1980s Virginia was widely thought to be the only source of distinct crystals; there are now at least 27 other localities. The specimens are highly valued by collectors. The crystals, forming a druse over the mother rock, are very small; 1 mm (0.04 inches) is considered large. In 1912, the first deposit of distinct, single-crystal turquoise was discovered in Lynch Station, Campbell County, Virginia. The Nevada material is noted for its often attractive brown or black limonite veining, producing what is called "spiderweb matrix".
Nevada is the country's other major producer, with an estimated 75–100 mines opened over the state's history. Arizona is currently the most important producer of turquoise by value, with the vivid Bisbee Blue being a good example of the state's natural endowment; much of the Arizona material is recovered as a byproduct of copper mining. While quite fine material—rivalling Iranian material in both colour and durability—is sometimes found, most American turquoise is of a low grade (called "chalk turquoise"); high iron levels mean greens and yellows predominate, and a typically friable consistency precludes use in jewellery in the turquoise's untreated state. The turquoise occurs as vein or seam fillings, and as compact nuggets; these are mostly small in size.
Only one mine in California, located at Apache Canyon, operates at a commercial capacity today. Cerrillos, New Mexico is thought to be the location of the oldest mines; prior to the 1920s, the state was the country's largest producer; it is more or less exhausted today. The deposits of California and New Mexico were mined by pre-Columbian Native Americans using stone tools, some local and some from as far away as central Mexico. The Southwest United States is a significant source of turquoise; Arizona, California (San Bernardino, Imperial, and Inyo counties), Colorado (Conejos, El Paso, Lake, and Saguache counties), New Mexico (Eddy, Grant, Otero, and Santa Fe counties) and Nevada are (or were) especially rich.
This rock is called Eilat stone and is often referred to as Israel's national stone: it is worked by local artisans for sale to tourists. In proximity to nearby Eilat, Israel, an attractive intergrowth of turquoise, malachite, and chrysocolla is found. Often referred to as Egyptian turquoise, Sinai material is typically the most translucent, and under magnification its surface structure is revealed to be peppered with dark blue discs not seen in material from other localities. The colour of Sinai material is typically greener than Iranian material, but is thought to be stable and fairly durable.
In the rainy winter months, miners face a risk from flash flooding; even in the dry season, death from the collapse of the haphazardly exploited sandstone mine walls is not unheard of. Large-scale turquoise mining is not profitable today, but the deposits are sporadically quarried by Bedouin peoples using homemade gunpowder. Copper and iron workings are present in the area. The turquoise is found in sandstone that is, or was originally, overlain by basalt.
The former mine is situated about 4 kilometres from an ancient temple dedicated to Hathor. The two most important of these mines, from a historic perspective, are Serabit el-Khadim and Wadi Maghareh, believed to be among the oldest of known mines. There are six mines in the region, all on the southwest coast of the peninsula, covering an area of some 650 km². Since at least the First Dynasty (3,000 BCE), and possibly before then, turquoise was used by the Egyptians and was mined by them in the Sinai Peninsula, called "Country of Turquoise" by the native Monitu.
Iranian turquoise has been mined and traded abroad for centuries, and was probably the source of the first material to reach Europe. Although it is commonly marred by whitish patches, its colour and hardness are considered superior to the production of other localities. Iranian turquoise is often found replacing feldspar. These workings, together with those of the Sinai Peninsula, are the oldest known.
A weathered and broken trachyte is host to the turquoise, which is found both in situ between layers of limonite and sandstone, and amongst the scree at the mountain's base. This "perfect colour" deposit is restricted to a mine-riddled, 2,012-metre mountain peak of Ali-mersai, 25 km from Mashhad, the capital of Khorasan province, Iran. For at least 2,000 years, the region once known as Persia, has remained the most important source of turquoise, for it is here that fine material is most consistently recovered. However, turquoise is often recovered as a byproduct of large-scale copper mining operations, especially in the United States.
Most are worked by hand with little or no mechanization. These are all small-scale, often seasonal operations, owing to the limited scope and remoteness of the deposits. Turquoise was among the first gems to be mined, and while many historic sites have been depleted, some are still worked to this day. Intergrowth with other secondary copper minerals such as chrysocolla is also common.
Odontolite is fossil bone or ivory that has been traditionally thought to have been altered by turquoise or similar phosphate minerals such as the iron phosphate vivianite. Turquoise may also pseudomorphously replace feldspar, apatite, other minerals, or even fossils. Stalactite forms have been reported. Typically the form is vein or fracture filling, nodular, or botryoidal in habit.
Crystals, even at the microscopic scale, are exceedingly rare. Turquoise is nearly always cryptocrystalline and massive and assumes no definite external shape. That said, there are reports of two phase fluid inclusions within turquoise grains that give elevated homogenization temperatures of 90 to 190 oC that require explanation. This hypogene process is applicable to the original copper sulfide deposition; however, it is difficult to account for the many features of turquoise occurrences by a hypogene process.
As the solutions cool, turquoise precipitates, lining cavities and fractures within the surrounding rock. Initially at high temperature, these solutions rise upward to surface layers, interacting with and leaching essential elements from pre-existing minerals in the process. The hypogene hypothesis, which holds that the aqueous solutions originate at significant depth, from hydrothermal processes. Although the features of turquoise occurrences are consistent with a secondary or supergene origin, some sources refer to a hypogene origin.
Typically turquoise mineralization is restricted to a relatively shallow depth of less than 20 m, although it does occur along deeper fracture zones where secondary solutions have greater penetration. In some occurrences alunite, potassium aluminium sulfate, is a prominent secondary mineral. In the American southwest turquoise is almost invariably associated with the weathering products of copper sulfide deposits in or around potassium feldspar bearing porphyritic intrusives. Climate factors appear to play an important role as turquoise is typically found in arid regions, filling or encrusting cavities and fractures in typically highly altered volcanic rocks, often with associated limonite and other iron oxides.
For example, the copper may come from primary copper sulfides such as chalcopyrite or from the secondary carbonates malachite or azurite; the aluminium may derive from feldspar; and the phosphorus from apatite. As a secondary mineral, turquoise apparently forms by the action of percolating acidic aqueous solutions during the weathering and oxidation of pre-existing minerals. Turquoise may also be peppered with flecks of pyrite or interspersed with dark, spidery limonite veining. Despite its low hardness relative to other gems, turquoise takes a good polish.
Its streak is a pale bluish white and its fracture is conchoidal, leaving a waxy lustre. Turquoise is infusible in all but heated hydrochloric acid. Under longwave ultraviolet light, turquoise may occasionally fluoresce green, yellow or bright blue; it is inert under shortwave ultraviolet and X-rays. An absorption spectrum may also be obtained with a hand-held spectroscope, revealing a line at 432 nanometres and a weak band at 460 nanometres (this is best seen with strong reflected light).
A reading of 1.61–1.65 (birefringence 0.040, biaxial positive) has been taken from rare single crystals. The refractive index (as measured by sodium light, 589.3 nm) of turquoise is approximately 1.61 or 1.62; this is a mean value seen as a single reading on a gemmological refractometer, owing to the almost invariably polycrystalline nature of turquoise. The blue is attributed to idiochromatic copper while the green may be the result of either iron impurities (replacing aluminium) or dehydration. Colour is as variable as the mineral's other properties, ranging from white to a powder blue to a sky blue, and from a blue-green to a yellowish green.
The lustre of turquoise is typically waxy to subvitreous, and transparency is usually opaque, but may be semitranslucent in thin sections. With lower hardness comes lower specific gravity (high 2.90, low 2.60) and greater porosity: These properties are dependent on grain size. Its crystal system is proven to be triclinic via X-ray diffraction testing. Characteristically a cryptocrystalline mineral, turquoise almost never forms single crystals and all of its properties are highly variable.
Even the finest of turquoise is fracturable, reaching a maximum hardness of just under 6, or slightly less than window glass. . This is thought to have arisen from a misconception: turquoise does not occur in Turkey but was traded there, and the gem became associated with the country in the West. The word turquoise is very old and likely is derived from the French pierre turquoise, meaning Turkish stone.
In recent times turquoise—like most other opaque gems—has had its popularity undermined by the introduction of treatments, imitations, and synthetics onto the market, some difficult to detect even by experts. It is rare and valuable in finer grades and has been enjoyed as a gem and ornamental stone for thousands of years owing to its unique hue. Turquoise (or turquois) is opaque, blue-to-green hydrated copper aluminium phosphate mineral according to the chemical formula CuAl6(PO4)4(OH)8·5H2O.