Harder than the tourmaline, turquois, or opal, as hard as the chrysolite, and nearly as hard as the garnet or emerald, there is no reason why the crystallized varieties, such as amethyst, cairngorm, false topaz, chrysoprase, and even the cat’s-eye and finer onyxes, should not be classed among the precious stones. Some more plentiful and less beautiful varieties of quartz are not valuable, and they take the same position in the quartz family that the huge imperfect crystals do in the beryl group. Whenever the specimen is sufficiently beautiful to be cut and polished for setting in jewelry, it should be included under the precious stones. Quartz crystallizes in the rhombohedral system, and many varieties are found massive and compact. The cleavage is indistinct but can sometimes be found by plunging a heated crystal into cold water. The hardness of quartz is 7; specific gravity 2.5 to 2.8, the purest kinds being 2.65; the lustre is vitreous to resinous, and fracture conchoidal. Quartz is tough, brittle, and feels cold; it becomes positively electric by rubbing, shows phosphorescence in the dark, and gives sparks if struck with another piece of quartz or with steel. Quartz is transparent to translucent, semi-translucent to opaque, doubly refractive, and does not melt before the ordinary blow-pipe, but may be melted with the oxyhydrogen blow-pipe. It also melts with soda to a clear glass, and is soluble in fluohydric acid. Quartz is composed of pure silica Oxygen 53 Silicon 47 Some of the impure varieties contain oxide of iron, carbonate of lime, clay, and other minerals. CRYSTALLIZED QUARTZ. Colorless quartz or pure rock-crystal is found in many parts of the world, notably in Switzerland, Dauphiny, Piedmont, the Carrara quarries in Italy, Canada; in Herkimer County, New York, and on the shores of Lake George, in the same place; at Hot Springs, Arkansas; and along the beach of Long Branch, Cape May, and many other places. Rock-crystal, commercially known as Bohemian diamond, occidental diamond, Lake George diamond, rhinestone, pebble, etc., etc., is colorless and transparent. This stone is largely used for optical purposes, and is also sometimes cut into brilliants to imitate the diamond. While rock-crystal is considerably harder than strass or paste, it lacks, however, the brilliancy of the fine-composition imitation diamond. Besides being much softer, the paste is often heavier than the crystal, because of the quantity of lead and other minerals used in its composition. AMETHYST. Amethystine quartz or amethyst varies in color from light to clear-dark purple, sometimes nearly black, and from light to dark bluish-violet. The coloring of the stone is supposed to be due to manganese.