Garnet.—A mineral having many varieties, differing in color and in their constituents, but with the same general chemical formula. The commonest color is red; the luster is vitreous, or glassy; and the hardness is greater than that of quartz, about half as hard as the diamond. Besides the red varieties there are also white, green, yellow, brown and black ones.
The garnet is a silicate with various bases. The transparent red varieties are used as gems. The garnet was the carbuncle of the ancients. Garnet is a very common mineral in gneiss and mica slate.
The finest specimens of red garnets come from Arizona and a single carat stone is worth about two dollars. A green variety that comes from Russia is worth about half as much as the diamond.
Heliotrope or bloodstone.—A green siliceous stone sprinkled with jasper, as if with blood, whence the name.
Hyacinth.—A red variety of zircon, sometimes used as a gem. It resembles closely a dark Spanish topaz, and is worth a little more than the garnet.
Indicolite.—A variety of tourmaline of an indigo-blue color.
Iolite.—A silicate of alumina, iron, and magnesia, having a bright blue color and a vitreous or glassy luster. It is remarkable for its dichroism, and is also called dichroite.
Jacinth.—Same as [hyacinth].
Jade.—A stone commonly of a pale to dark green color, but sometimes whitish. It is hard and very tough, capable of a fine polish, and is used for ornamental purposes and for implements, especially in eastern countries and among many primitive peoples.
Jasper.—An opaque, impure variety of quartz, of red, yellow, and other dull colors, breaking with a smooth surface. (See [quartz].)