This is a group of differently colored minerals with similar chemical composition. The name derives from the Latin for grain because of the grain because of the rounded crystals. Garnet, in the popular sense, is understood to mean red “garnets”, almandine and pyrope. Data common to all garnets :
of streak: white
Fracture: Conchoical, splintery, brittle
Crystal system : Isometric ; rhombic, dodecahedron, icositetrahedron
Double refraction: Only rhodolite
: Red with brown tint
Mohs’ hardness : 7 – 7.5
Specific gravity : 3.65 – 3.80
Chemical composition: Magnesium aluminium silicate
Refractive index : 1.730 – 1.760
(Greek – fiery) is so-called because of its red color. It was the fashion stone
of the 18th and 19th centuries. Main deposits are in Czechoslovakia, South Africa,
Australia. Confused with almandine, spinel, ruby.
Rhodolite : rose-red or pale violet type of pyrope. Found in the US (North Carolina), Sri Lanka, Brazil. Zambia and Tanzania.
: Red with violet tint
Mohs’ hardness : 7.5
Specific gravity : 3.95 – 4.20
Chemical composition : iron aluminium silicate
Refractive index : 1.78 – 1.81
Its named is derived from the town in Asia Minor. In order to lighten the color, the underside of some cut stones is hollowed out. Main deposits are in Sri Lanka, India, Afghanistan and Brazi, Austria and Czechoslovakia. Can be confused with pyrope, ruby and spinel.
: Orange to red brown
Mohs’ hardness : 7-7.5
Specific gravity : 4.12 – 4.20
Chemical composition : Manganese aluminium silicate
Refractive index : 1.795 – 1.815
Its name derived from a former occurrence in Spessart, Germany. Now found in Sri Lanka, Brazil, US, Malagasy Republic and Sweden. Can be confused with hessoinite.
: Green, emerald green
Mohs’ hardness : 6.5 – 7
Specific gravity : 3.82 – 3.85
Chemical composition : calcium iron silicate
Refractive index : 1.888 – 1.889
Demantiod (diamond-like luster) is the most valuable garnet. Found in the Urals, it can be confused with grossular, peridot, emerald, spinel, tourmaline and idocrase.
Melanite is opaque, a black variety of andradrite. Found in Germany (Kaiserstuhl), France and Italy.
Topazolite is a lemon-yellow variety (similar to topaz) of andradite. Only small crystals are found in Switzerland (Zermatt) and the Italian Alps.
: Emerald green
Mohs’ hardness : 7.5
Specific gravity : 3.77
Chemical composition : Calcium chromium silicate
Refractive index : about 1.870
Named after Russian statesman. Deposits are in Urals, Finland, Poland, India, the US and Canada. Can be confused with emerald.