QUARTZ (AIHG. quart, Ger. Quar:, rock crystal, quartz). A mineral composed of silica or silicon dioxide, crystallizing in the hexagonal system. It is very hard, scratching glass readily, and has a specific gravity of from 2.5 to 2.8. de pending upon the amount of impurity present. When pure it is colorless and perfectly trans parent, but it often has some shade of yellow. red, brown, green, blue, or black. By friction it becomes positively electrified. It is a very alum dant and widely distributed mineral, largely composing the sands found on beaches and being also a constituent of most rocks. (See ROCKS.) The mineral species includes two important groups: those that are crystallized and have a vitreous lustre, called 'pheno-erystalline,' and those that are massive and fiint-like, called 'crypto-crystalline! The pheno-crystalline varieties of quartz in clude amethyst, asteriated or star quartz, aven turine, cairngorm, moriou or smoky quartz, eat's-eye, citrone or false, Saxon, Scottish or Spanish topaz. ferruginous quartz, or rubasse, (sometimes called 'anemia' or 'Mont Blanc ruby), hyaline, milky or greasy quartz, rock crystal (in cluding the Brazilian pebble, 'Lake George dia monds.' etc.), rose quartz, sagenitie quartz, and sapphirine, or siderite. The erypto-crystalline varieties include agate ('banded' or 'eye agates,' `fortification' or 'ruin agates.' dendritic agate,
moss agate, agatized wood, etc.), basanite ly dian stone or touchstone), beekite, bloodstone or heliotrope, carnelian, chalcedony, chrysoprase, hornstone. jasper. onyx, plasma, prase, sard, and sardonyx. In addition to the fore going should he mentioned quartz rock or quartz ite (q.v.), which is a sedimentary sandstone con verted into a very hard compact rock by meta morphic action. Although it is distinctly granu lar, the grains seem to melt into each other, or to be enveloped in a homogeneous paste. Of similar nature are the different varieties of pseudomorphons quartz, such as the agatized wood and beekite previously mentioned.
The common variety of crystallized quartz is employed in the arts as an abrasive, principally in the manufacture of sandpaper. It is also crushed and used for polishing marble and as a filler for wood. For the latter purpose it is ground to an impalpable powder and combined with japans or oils to make a paste which is then applied to the surface of the wood. Quartz sands are of importance in the manufacture of glass, refractory brick, mortar, cements. etc. The oc currence of quartz in the form of veins is note worthy from the fact that such veins are the sourees of many of the valuable metals. includ ing gold, silver, copper. and lead. ) See ORE DE