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GarnetEncyclopedia Index

The gaet group of minerals show crystals with a habit of rhombic dodecahedrons and trapezohedrons. They are nesosilicates with the same general formula, A3B2(SiO4)3 in which the A site is usually occupied by divalent cations (Ca, Mg, Fe2+) and the B site by trivalent cations (Al, Fe3+, Cr). The chemical elements in gaet include calcium, magnesium, aluminium, iron2+, iron3+, chromium, manganese, and titanium. Gaets 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 "gaet" 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 gaet crystals.Gaets 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 gaet 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 gaets are by far the rarest gaets 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 gaets are a mix of spessartine and pyrope, as are Malaya gaets. The color change of these new gaets 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 gaets will match Alexandrite prices or even exceed them as the color change is often better and these gaets are much rarer. The blue color-change type is mainly caused by relatively high amounts of vanadium (about 1 wt.% V2O3).Six common varieties of gaet 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 gaets make up two solid solution series; 1. pyrope-almandine-spessarite and 2. uvarovite-grossularite-andradite.Gaet is the birthstone for January, and has been used since the Bronze Age.

Uses of gaets

Pure crystals of gaet are used as gemstones. Gaet sand is a good abrasive, and a common replacement for silica sand in sand blasting. Mixed with very high pressure water, gaet is used to cut steel and other materials in water jets. Pyrope varieties are used as kimberlite indicator minerals in diamond prospecting.Gaets are very abundant in the lower crust and mantle and thus play an important role in geochemical understanding of the Earth.The gaet is the official mineral and color of Bates College.The gaet is the birthstone for January. It is a symbol of faith and trust and when given as a gift is a token of devotion and loyalty. The mineral was used in the 13th century as an insect repellent and to ward off evil spirits. The ancient Egyptians placed them in tombs as payment to the gods for a spirit's safe passage to the afterlife.