Garnet

A pic of the Garnet Crystal

Six common varieties of garnet are recognized based on their chemical composition. They are pyrope, almandine or carbuncle, spessartite, grossularite (varieties of which are hessonite or cinnamon-stone and tsavorite), uvarovite and andradite. The garnets make up two solid solution series; 1. pyrope-almandine-spessarite and 2. uvarovite-grossularite-andradite. Garnet is the birthstone for January, and has been used since the Bronze Age.

Garnets are most commonly red in color but can be found in a variety of colors, including purple, red, orange, yellow, green, brown, black, or colorless. The lack of a blue garnet was remedied in 1990s following the discovery of color-change blue to red/pink material in Bekily, Madagascar but these stones are very rare. Color-change garnets are by far the rarest garnets except uvarovite, which does not come in cuttable sizes. 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. By composition, these garnets are a mix of spessartine and pyrope, as are Malaya garnets. 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 U.S. dollars per carat. 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 blue color-change type is mainly caused by relatively high amounts of vanadium (about 1 wt.% V2O3).

The garnet group of minerals show crystals with a habit of rhombic dodecahedrons and trapezohedrons. They are nesosilicates with the same general formula, X3Y2(SiO4)3 in which the X site is usually occupied by divalent cations (Ca, Mg, Fe2+) and the Y site by trivalent cations (Al, Fe3+, Cr). The chemical elements in garnet include calcium, magnesium, aluminium, iron2+, iron3+, chromium, manganese, and titanium. Garnets show no cleavage and a dodecahedral parting. Fracture is conchoidal to uneven; some varieties are very tough and are valuable for abrasive purposes. hardness is 6.5-7.5, specific gravity is 3.1-4.3, lustre is vitreous to resinous, and they can be transparent to opaque. The name "garnet" comes from the Latin granatus ("grain"), possibly a reference to the malum granatum ("pomegranate"), a plant with red seeds similar in shape, size, and color to some garnet crystals.