Garnet

garnet, name applied to a group of isomorphic minerals crystallizing in the cubic system. They are used chiefly as gems and as abrasives (as in garnet paper). The garnets are double silicates; one of the metallic elements is calcium, magnesium, ferrous iron, or manganese and the other aluminum, ferric iron, or chromium. Six varieties (of which there are also intermediate forms) are distinguished according to composition-grossularite (calcium-aluminum), pyrope (magnesium-aluminum), spessartite (manganese-aluminum), almandite (iron-aluminum), andradite (calcium-iron), and uvarovite (calcium-chromium). Grossularite occurs commonly in a red, green, yellow, or brown shade, depending on the impurities; if pure it would be colorless.
The yellow and brown stones, coming chiefly from Sri Lanka, are used as gems under the names essonite (or hessonite) and cinnamon stone; sometimes they are miscalled hyacinth. Grossularite is found also in the Transvaal, in Mexico, and in Oregon. The most popular variety of garnet is the ruby-red pyrope from Bohemia, S Africa, and Arizona, sold as Cape ruby and Arizona ruby. Rhodolite, a mixture of pyrope and almandite from North Carolina, is rose-red or purple.