Garnet
Garnet actually is a group or family of mineral species with related chemical compositions in cubic form that can differ widely in their physical properties and appearance.  This difference in appearance provides choice of color and economy for every pocketbook.  Garnet occurs in every color except blue, although there are change-of-color garnets from East Africa that can display a blue color when viewed through transmitted light.  The name “garnet” is derived from the Latin word for grain, referring to the rounded crystals of Almandite garnet, which exhibit a similarity to pomegranate seeds. Garnet is the birthstone for January.
 
The species and varieties in the garnet family consist of Pyrope - Pyrope, Rhodolite; Almandite - Star Almandite; Spessartite - Spessartite, Malaia; Uvarovite; Grossularite - Tsavorite, Hessonite, Hydrogrossularite; and Andradite - Demantoid, Topazolite, Melanite, Iridescent Andradite garnets.  The type of garnet depends upon physical, optical, and chemical properties.  These different species tend to inter-mix due to their closely related chemical structures. The properties of the different species of garnet are not constant and can very considerably.  Listed below are descriptions of the different garnet species and their properties.
 
Garnets are composed of two sub-groups consisting of Pyralspite for Pyrope, Almandite and Spessartite, and Ugrandite for Uvarovite, Grossularite and Andradite.  The Pyralspite sub-group of garnets contains aluminum in its chemistry and readily inter-mixes.  The Ugrandite series of garnets are closely related due to the presence of calcium as an essential element, rather than aluminum.
 
Pyrope and Rhodolite Garnet Species
 
Often employed in “Bohemian Garnet” antique and reproduction jewelry, deep red Pyrope garnets generally occur in small sizes (under 2 carats), and differ from other garnets in that they are volcanic rather than metamorphic in origin.  A small amount of chromium is responsible for the often intense red color.  Pyrope gets its name from the Greek word for “fiery.”  Because magnesium atoms are similar in size to iron atoms, Pyrope garnets readily mix chemically with Almandite garnets and become lighter and more purplish-red in color as more Almandite is added.  This combination of Pyrope and Almandite garnets results in a new species called Rhodolite garnet.  Rhodolite garnet is named for the Greek rhodos for rose.  Pyrope and Rhodolite garnets are found in Burma (Myanmar), China, Madagascar, South Africa, Tanzania, and the United States (Arizona/New Mexico border).
 
Pyrope and Rhodolite Garnet Properties
Species:  Pyrope, Rhodolite
Chemical Composition:  Mg3Al2Si3O12
Colors:  Pyrope - Red, Brownish-Red; Rhodolite - Violetish-Red, Brownish-Red
Hardness:  7 - 7 ½
Crystal System:  Cubic
Refractive Index:  1.714 to over 1.742, 1.74 normal 
Specific Gravity:  3.78 (+.09, -.16)
 
 
Almandite Garnet Species
Almandite, Star-Almandite Varieties
 
Typically slightly brownish-red, Almandite garnets can occur in large sizes and probably are the most frequently used garnets in jewelry.  Almandite garnets are faceted or cut as a cabochon (with a polished convex surface and no facets), and were often used in mid-Victorian sets of jewelry because the color was easy to match with other stones and due to the fact that they occur in large sizes.  This style of garnet jewelry reached the height of popularity during the 1860s.  Cutting Almandite garnets in a cabochon form with the back hollowed out was employed to lighten the typically brownish- to violetish-red color so the stone could be appreciated.  Star Almandite garnets display a 4-rayed star and can occur in fairly large crystals.  These star garnets are found in India and the United States (Idaho).  Sources of gem-quality Almandite garnet occur in India, Tanzania, Madagascar, Brazil, Baja California, and British Columbia, Canada.  Large beautifully formed crystals occur in Alaska and are popular tourist’s trophies.
 
Almandite Garnet Properties
Species:  Almandite
Varieties:  Almandite, Star-Almandite
Chemical Composition:  Fe3Al2Si3O12
Colors:  Orangish-Red, Brownish-Red, Purplish-Red
Hardness:  7 - 7 ½
Crystal System:  Cubic
Refractive Index:  1.790 (+/- .030)
Specific Gravity:  4.05 (+.25, -.12)
 
Spessartite Garnet Species
Spessartite, Malaia, Cats’ Eye Spessartite Varieties


One of the most beautiful orange gems available, Spessartite is named for its initial discovery in the Spessart Forest district of Bavaria in Germany.  Because supply has traditionally been so uncertain, Spessartite was considered more of a collector’s gem until 1991, when a deposit of several hundred kilos of very fine quality was discovered in northwest Namibia.  The Namibian deposit produces stones of exceptional color purity, with little brown or yellow modifying hues (due to the lack of iron), and exhibits a brilliant orange color.  In 1998 and early 1999, Spessartite began to appear from Nigeria.  Although tending to be more included and slightly more yellow in color than the Namibian material, it can be produced in fairly large (10+ carat) sizes and the availability is good.  A mixture of Spessartite with Pyrope Garnet produces a pinkish- to brownish-orange trade variety known as Malaia Garnet, also from East Africa.  Spessartite Garnets can be found in Brazil, Sri Lanka (Ceylon), Burma (Myanmar), Madagascar, Australia, and the United States (Virginia and California).
 
Spessartite Garnet Properties
Species:  Spessartite
Varieties:  Spessartite, Malaia, Cats’ Eye Spessartite
Chemical Composition:  Mn3Al2Si3O12
Colors:  Spessartite - Orange, Yellowish-Orange, Brownish-Orange; Malaia - Orange, Pinkish-Orange, Reddish-Orange
Hardness:  7 to 7 ½
Crystal System:  Cubic
Refractive Index:  1.810 (+.004, -.020)
Specific Gravity:  4.15 (+.05, -.03)
 
Uvarovite Garnet Species

Uvarovite Garnet is an emerald green garnet colored by chromium that would be very popular in jewelry if it occurred in large enough crystals to facet or polish.  Only seen as clusters of very small crystals or druzy surfaces covered with minutely small gorgeous green crystals, Uvarovite is sometimes seen in artistic free-form styles of jewelry.  Uvarovite is found in Finland, India, Canada, Poland, Russia (the Ural Mountains), and the United States (California).
 
Uvarovite Garnet Properties
Species:  Uvarovite
Varieties:  Uvarovite
Chemical composition:  Ca3Cr2Si3O12
Color:  Slightly Bluish- to Yellowish-Green
Hardness:  7 ½
Crystal System:  Cubic
Refractive Index:  1.87
Specific Gravity:  3.77
 
Grossularite Garnet Species
Tsavorite, Hessonite, Hydrogrossularite Varieties


Grossularite Garnets occur in a wide range of colors:  colorless, yellow, orange, red, purple, green, and pink, and occur in two varieties:  Tsavorite and Hessonite, and one sub-group:  Hydrogrossularite.  The most valued Grossularite Garnet is the lovely green Tsavorite Garnet variety, discovered in the early 1970s by the late British geologist Campbell Bridges on the border of Tanzania and Kenya, and named after Tsavo National Park, which is nearby.  This deposit, known as the Scorpion Mine, is the primary deposit for this type of garnet and is not found in any substantial quantity anywhere else on earth.  When green garnets were first put on the market, most people had never heard of them; it was Tiffany & Co. who first successfully marketed this gem.  Sizes can occur up to 18 carats, but tend to be smaller than 5 carats.  The green of this garnet ranges from bluish- to yellowish-green and the stone overall displays a very bright countenance.  Hessonite is a yellowish- to brownish-orange garnet variety, sometimes called “cinnamon stone,” which can resemble the more expensive Spessartite garnet.  Hessonite is found in sizes ranging from 1 to 15 carats in Sri Lanka (Ceylon), Brazil, India, Canada, Madagascar, Tanzania, and the United States.  A sub-species of grossularite garnet is Hydrogrossularite garnet, having added water to the chemical composition.  This type of garnet always appears translucent-to-opaque and is often sold as “Transvaal Jade.”  Hydro-grossular garnet also rarely appears in a pink form and is mined in South Africa, Burma (Myanmar), and Zambia.
 
Grossularite Garnet Properties
Species:  Grossularite
Varieties:  Grossularite, Tsavorite, Hessonite, Hydrogrossularite 
Chemical Composition:  Ca3Al2Si3O12
Colors:  Colorless, Yellow Brown, Green, Pink, Red, Purple, Orange
Hardness:  Grossularite -7 to 7 ½, Hydro-Grossular - 7
Crystal System:  Cubic
Refractive Index:  1.740 (+.020, -.010)
Specific Gravity:  3.61 (+.12, -.04)
 
Andradite Garnet Species
Demantoid, Topazolite, Melanite, Iridescent Andradite Varieties


The Demantoid Garnet variety is the most highly prized of all the garnets.  Bright green in color, with the addition of some chromium and possessing a dispersion greater than that of diamond (Demantoid Garnet dispersion is .057 and diamonds’ .044), Demantoid Garnet for many years was found only in antique jewelry, as the original source in Russia was not accessible during the Cold War.  Discovered in 1868 in the Ural Mountains in Russia, cut stones larger than 2 carats are very rare, with most stones being in the one carat or smaller size range.  Cut stones over 5 carats are considered museum pieces.  Another deposit of Demantoid was eventually found in the same area of the Urals and mined from the late 1990s to the present day.  Lesser quality Demantoid Garnets are mined in Iran, Italy and Namibia, but always are of a lesser quality compared to their Russian counterparts.  Peculiar inclusions, almost always present and diagnostic in Demantoid Garnet, are “horsetail” inclusions, actually chrysotile fibers arranged in a somewhat circular formation.  A yellow variety of Andradite is called “Topazolite,” and is found in Italy and Switzerland; a black variety called “Melanite” exists, but neither is often seen in fine jewelry.  A new variety of Iridescent Andradite Garnet has been found in Mexico in smaller sizes (under 5 carats); it exhibits a fantastic iridescent or rainbow-like quality over the entire stone surface, with the body color of the stone itself being translucent to opaque brownish-yellow.  These iridescent garnets are fairly new to the marketplace and so have not yet garnered a lot of exposure. 
 
Andradite Garnet Properties
Species:  Andradite
Varieties:  Demantoid, Topazolite, Melanite, Iridescent Andradite
Chemical composition:  Ca3Fe2(SiO4)3
Colors:  Green, Yellow, Yellowish-Brown, Black 
Hardness:  6 ½ to 7
Crystal System:  Cubic
Refractive Index:  1.888 (+.007, -.033)
Specific Gravity:  Demantoid, Topazolite and Iridescent Andradite - 3.84 (+/-.03), Melanite - 3.90 (+/-.20)

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