Garnet, the
January birthstone, derived its name from the Latin word granatus, meaning
like a grain, which refers to the mode of occurrence wherein crystals
resemble grains or seeds embedded in the matrix. Garnet is a family of
minerals having similar physical and crystalline properties. They all have
the same general chemical formula, , where A can be calcium, magnesium,
ferrous iron, or manganese, and B can be aluminum, ferric iron, or
chromium, or in rare instances, titanium.
The formulas and names of common garnet species are:
Some rare species
of garnet are known that illustrate the wide range of substitution that
the garnet crystal structure can accommodate. They include:
There are a number of trade and variety names for garnet, most of these
names are for particular colors of a specie. Hessonite is the variety name
for a fine orange, cinnamon brown, or pinkish variety of grossularite,
while tsavorite is the trade name for fine dark green grossularite.
Melanite is a black titanium bearing variety of andradite and demantoid is
a rich green variety. Malaya is a trade name for a pyrope-spessartite that
varies in color from red, through shades of orange and brownish orange to
peach and pink. Rhodolite is a purplish red pyrope-almandite solid
solution garnet. Fine-quality pyrope garnets from Czechoslovakia are often
called Bohemian garnets. Almandite and almandite-pyrope solid solution
garnets are the best abrasive types, but andradite, grossularite, and
pyrope also are used. All species of garnet have been used as gemstones.
