Garnet

The garnet is the official mineral and color of Bates College. One half is also:. Garnets are very abundant in the lower crust and mantle and thus play an important role in geochemical understanding of the Earth. equals 1 for detailed discussion of a related case. Pyrope varieties are used as kimberlite indicator minerals in diamond prospecting. It's a common trap to believe these expressions represent distinct numbers: see the proof that 0.999.. Garnet sand is a good abrasive. It has a similar pair of expansions in any even base.

Pure crystals of garnet are used as gemstones. One half has two different decimal expansions, the familiar 0.5 and the recurring 0.49999999.. When doped with neodymium (Nd³⁺), these YAl-Garnets are useful as the lasing medium in lasers. and in the formula for computing magic constants for magic squares. Yttrium aluminium garnet (YAG), Y₃Al₂(AlO₄)₃, is used for synthetic gemstone. One half also figures in the formula for calculating figurate numbers, such as triangular numbers and pentagonal numbers:. One example for this is gadolinium gallium garnet, Gd₃Ga₂(GaO₄)₃, which is synthesized for use in magnetic bubble memory. For instance, the area S of a triangle is computed.

By substituting specific sites with rare earth elements, for example, interesting magnetic properties can be obtained. It is the fraction occurring most often in mathematical equations, recipes, measurements, etc. The iron ions in the two coordination sites exhibit different spins, resulting in magnetic behaviour. One half is the irreducible fraction resulting from dividing one by two (½), or any number by its double; multiplication by one half is equivalent to division by two. In yttrium iron garnet (YIG), Y₃Fe₂(FeO₄)₃, the five iron(III) ions occupy two octahedral and three tetrahedral sites, with the yttrium(III) ions coordinated by eight oxygen ions in an irregular cube. One of the few fractions which is commonly expressed in natural languages by suppletion rather than regular derivation; compare English one half with regular formations like one sixth from six. It is used as an indicator mineral in the search for diamonds. It also gets its own point in some early extensions of ASCII at 189; and in Unicode, it gets its own code point at 189 in the C1 Controls and Latin-1 Supplement block, and a cross-reference in the Number Forms block, which contains some other fractions.

Knorringite is basically pyrope with a very high chromium content and is often found in kimberlites. One of the few fractions to get a key of its own on typewriters. Garnet with high knorringite content may be generated only under high pressure. Pure knorringite never occurs in nature. Knorringite is a magnesium chromium garnet with the formula Mg₃Cr₂(SiO₄)₃.

It is found in crystalline marbles and schists in the Ural mountains of Russia and Outukompu, Finland. This is a rather rare garnet, bright green in color, usually found as small crystals associated with chromite in peridotite, serpentinite, and kimberlites. Uvarovite is a calcium chromium garnet with the formula Ca₃Cr₂(SiO₄)₃. This garnet was discovered in the 1960s in the Tsavo area of Kenya, from which the gem takes its name.

One of the most sought after varieties of gem garnet is the fine green grossular garnet from Kenya and Tanzania called tsavorite. Grossularite is found in contact metamorphosed limestones with vesuvianite, diopside, wollastonite and wernerite. Because of its inferior hardness to zircon, which the yellow crystals resemble, they have also been called hessonite from the Greek meaning inferior. Other shades include cinnamon brown (cinnamon stone variety), red, and yellow.

The name grossularite is derived from the botanical name for the gooseberry, grossularia, in reference to the green garnet of this composition that is found in Siberia. Grossularite is a calcium-aluminium garnet with the formula Ca₃Al₂(SiO₄)₃, though the calcium may in part be replaced by ferrous iron and the aluminium by ferric iron. Topazolite is a golden yellow variety and melanite is a black variety. Demantoid has been called the "emerald of the Urals" from its occurrence there, and is one of the most prized of garnet varieties.

Andradite is found both in deep-seated igneous rocks like syenite as well as serpentines, schists, and crystalline limestone. The recognized subvarieties are topazolite (yellow or green), demantoid (green) and melantite (black). Andradite is a calcium-iron garnet, Ca₃Fe₂(SiO₄)₃, is of variable composition and may be red, yellow, brown, green or black. Violet-red spessartites are found in rhyolites in Colorado and Maine.

Spessartite of a beautiful orange-yellow is found in Madagascar. It occurs most often in granite pegmatite and allied rock types and in certain low grade metamorphic phyllites. Its name is derived from Spessart in Bavaria. Spessartite or spessartine is manganese aluminium garnet, Mn₃Al₂(SiO₄)₃.

The garnets from mantle derived rocks, peridotites and eclogites, commonly contain a pyrope variety. Pyrope is an indicator mineral for high pressure rocks. The color of these blue garnets is not like sapphire blue in subdued daylight but more reminiscent of the grayish blues and greenish blues sometimes seen in spinel However in white LED light the color is equal to the best corn flower blue sapphire or D block tanzanite this is due to the blue garnets ability to absorb the yellow component of the emitted light. Another intriguing find is the blue color-change garnets from Madagascar, a pyrope spessatine mix.

Pyrope has nicknames of Cape ruby, Arizona ruby, California ruby, Rocky Mountain ruby, and Bohemian garnet from the Czech Republic. A variety of pyrope from Macon County, North Carolina is a violet-red shade and has been called rhodolite, from the Greek meaning "a rose." In chemical composition it may be considered as essentially an isomorphous mixture of pyrope and almandite, in the proportion of two parts pyrope to one part almandite. Transparent pyropes are used as gemstones. The color of pyrope varies from deep red to almost black.

It is ruby-red in color and chemically a magnesium aluminium silicate with the formula Mg₃Al₂(SiO₄)₃, though the magnesium can be replaced in part by calcium and ferrous iron. Pyrope, from the Latin pyropos, means similar to fire. Almandite has nicknames of Oriental garnet, almandine ruby, and carbuncle. Almandite occurs in metamorphic rocks like mica schists, associated with minerals such as staurolite, kyanite, andalusite, and others.

Chemically, almandite is an iron-aluminium garnet with the formula Fe₃Al₂(SiO₄)₃; the deep red transparent stones are often called precious garnet and are used as gemstones (being the most common of the gem garnets). The term "carbuncle" is derived from the Latin meaning "little spark." The name Almandite is a corruption of Alabanda, a region in Asia Minor where these stones were cut in ancient times. Almandite, sometimes called almandine, is the modern gem known as carbuncle (though originally almost any red gemstone was known by this name). .

Garnet is the birthstone for January, and has been used since the Bronze Age. uvarovite-grossularite-andradite. pyrope-almandine-spessarite and 2. The garnets make up two solid solution series; 1.

They are pyrope, almandine or carbuncle, spessartite, grossularite (varieties of which are hessonite or cinnamon-stone and tsavorite), uvarovite and andradite. Six common varieties of garnet are recognized based on their chemical composition. The blue color-change type is mainly caused by relatively high amounts of vanadium (about 1 wt.% V₂O₃). It is expected that blue color-change garnets will match Alexandrite prices or even exceed them as the color change is often better and these garnets are much rarer.

The color change of these new garnets is often more intense and more dramatic than the color change of top quality Alexandrite which is frequently disappointing, but still sells for many thousands of dollars (US) per carat. By composition, these garnets are a mix of spessartine and pyrope, as are Malaya garnets. In daylight, their color can be shades of green, beige, brown, gray and rarely blue, to a reddish or purplish/pink color in incandescent light. Color-change garnets are by far the rarest garnets except uvarovite, which does not come in cuttable sizes.

The lack of a blue garnet was remedied in 1990's following the discovery of color-change blue to red/pink material in Bekily, Madagascar but these stones are very rare. There is a misconception that garnets are only a red gem but in fact they come in a variety of colors including purple, red, orange, yellow, green, brown, black, or colorless. The name "garnet" comes from the Latin granatus, a grain possibly in reference to malum garanatum (pomegranate) a plant with red seeds similar in shape, size and color to some garnet crystals. Hardness is 6.5 - 7.5, specific gravity is 3.1 - 4.3, luster is vitreous to resinous, and they can be transparent to opaque.

Fracture is conchoidal to uneven; some varieties are very tough and are valuable for abrasive purposes. Garnets show no cleavage and a dodecahedral parting. The chemical elements in garnet include calcium, magnesium, aluminium, iron²⁺, iron³⁺, chromium, manganese, and titanium. They are nesosilicates with the same general formula, A₃B₂(SiO₄)₃.

The garnet group of minerals show crystals with a habit of rhombic dodecahedrons and trapezohedrons. Anthony, Gemologist. Lets Talk Gemstones by Edna B. Mineral Miners Garnet Info.

USGS Garnet locations - USA. Mineral galleries. Minerals.net. Mindat.org.

Color Encyclopedia of Gemstones ISBN 0442203330. Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., Wiley, ISBN 0471805807. Calderite: Mn₃Fe³⁺₂(SiO₄)₃. Majorite: Mg₃(Fe,Al,Si)₂(SiO₄)₃.

Knorringite: Mg₃Cr₂(SiO₄)₃. Magnesium or manganese in A site