Indian Gemological Identification

GARNET 

All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition

Properties

Garnet species are found in many colors including red, orange, yellow, green, purple, brown, blue, black, pink and colorless. The rarest of these is the blue garnet, discovered in the late 1990s in Bekily, Medagascar. It is also found in parts of the United States, Russia, Kenya, Tanzanite, and Turkey.

The blood color of PYROPE is due to its iron and chromium contest. It rarely has inclusions. This are found in volcanic rock. There are also other varieties of GARNET as SPESSARTINE, ALMANDINE, UVAROVITE, PINK OR GREEN GROSSULAR.

Hardness

Because the chemical composition of garnet varies, the atomic bonds in some species are stronger than in others. As a result, this mineral group shows a range of hardness on the Mohs scale of about 6.5 to 7.5. The harder species like almandine are often used for abrasive purposes.

Almandine

Almandine, sometimes incorrectly called almandite, is the modern gem known as carbuncle (though originally almost any red gemstone was known by this name).

Pyrope

Pyrope (from the Greek pyropos meaning "fire-eyed") is red in color and chemically an aluminium silicate with the formula Mg3Al2(SiO4)3.

Spessartine

Spessartine or spessartite is manganese aluminium garnet, Mn3Al2(SiO4)3. Its name is derived from Spessart in Bavaria.

Andradite

Andradite is a calcium-iron garnet, Ca3Fe2(SiO4)3, is of variable composition and may be red, yellow, brown, green or black.

Grossular

Grossular 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.

Uvarovite

Uvarovite is a calcium chromium garnet with the formula Ca3Cr2(SiO4)3. This is a rather rare garnet, bright green in color, usually found as small crystals associated with chromite in peridotite, serpentinite, and kimberlites.

Knorringite

Knorringite is a magnesium-chromium garnet species with the formula Mg3Cr2(SiO4)3. Pure endmember knorringite never occurs in nature. Pyrope rich in the knorringite component is only formed under high pressure and is often found in kimberlites. It is used as an indicator mineral in the search for diamonds.

Crystal Structure : Cubic

Composition       : Calcium Aluminum Silicate

Hardness           : 6.5 - 7.5

Refractive Index  : 1.73 – 1.76

Specific gravity   : 3.60 - 4.25