QUARTZ, the name given the native oxide of silicon, SiOl. It is a widely distributed min eral occurring not only in veins and segregated masses, but as a common constituent of igneous rocks. Detrital form sands, and when cemented, sandstones and quartzites. Owing to differences in color end- its use as a semi-precious stone, the names given varie ties of quartz are' many: All these varieties, however, are included in two classes, the plainly crystalline or vitreous, and' the obscurely cry's-. talline called crypto-crystalfine. All varieties have about the same 'hardness, seven, that' is, can scratch window glabs, and neatly the same specific gravity, 2.6. Pure quartr is fusible only at high temperatures. • Quartz crystalfizes in the rhiambohedral sys tem, generally as slit-sided prisms usually termi nated at each end by six-sided pyramids. 'Among the crystalline vartetietvoiltiartz -are rock crys tal, amethyst, smoky quartz,'rose quartz, milky quartz, the mineral being colorless when pure, but ranging thrbugh various shades of yellow, red, brown, blue and green 'to black when im pare. Colorless quartz; or rock crystal, is often cut into gem shapes au& said as Lake George diamonds, Brazil pebbles, etc. Perfectly clear crystals of larger size are hisably prized in Japan when cut and polished as,spheres. Recently de veloped uses of 'rock crystal are in the ture of fibres for •suspending the minute magnets and mirrors used as galvanometers and in the manufacture of spectrum tubes and test tubes, the quartz being • fused by the oxybydrogen blowpipe. Quartz fibres are used for galvanom eters because they show no torsion and the minors have no permanent set or deviation from the true position when at rest. Vessels made of fused quartz can be heated to a white heat and plunged into cold water without injury and on this account quartz tubes are used for study ing the spectra gases at high temperatures.
Of the colored varketies of crystalline quartz amethyst is clear,purple pr bluish-violet, and is popular as a gem ; rose quartz, which always occurs massive, is rose red or pink; yellow quartz, or citrine, is often called topaz by jewel ers, but may be distinguished from true topaz by its inferior hardness; smoky quartz, called also cairngorm stone, varies in color from smoky yellow to brownish black; milky quartz, white, nearly opaque and often with a greasy lustre, is of common occurrence in veins; sagen itic quartz has inclusions of needle-like crystals of rutile, actinolite, asbestos (cat's-eye) or black tourmaline ; sapphire quartz, indigo blue in color, is a rare variety. Many quartz crystals contain
small cavities partly filled with liquids, generally water, also inclusions of carbonic acid, either liquid or gaseous. The cryptocrystalline varie ties of quartz include chalcedony, and its varie ties, carnelian, chrysoprase, prase, plasma, agate, onyx and sardonyx; also flint, hornstone, touch stone and jasper. Chalcedony has a wax-like lustre, is translucent or transparent, and its color varies from white through pale brown to dark i brown or black, though it is occasionally blue; carnelian or sand, is a red or brownish-red chalcedony,• chrysoprase an apple-green variety; prase, a dull darker green • plasma, a leek green or emerald green; bloodstone, a dark green chalcedony with small red spots, like drops of blood; agate, a chalcedony with delicate parallel bands of color, or irregularly clouded color effects, the colors being white, red, brown or even blue, while moss agate contains moss-like forms caused by oxide of manganese;.in onyx the differently colored bands are straight and parallel; sardonyx is onyx containing bands of carnelian (said) ; flint differs from chalcedony in being more opaque, having a vitreous lustre, being generally gray or brown in color; it breaks with, a sharp cutting edge ; it was used by the early races of men for arrow beads, knives, etc.; hornstone resembles flint, but has a splintery fracture, and is often white; touch stone, known also as basanite or Lydian stoat, a black hornstate or jasper, used for testing the purity of precious metals by rubbing them on it jasper differs from the preceding varieties in being entirely opaque; it is often red, yellow or brown.
Common milky quartz is used for a variety of purposes. In metallurgical operations it is used as a flux in smelting iron and copper ores; when finely crushed it is used by portelain manufacturers for making glazes, quartz sand and ground pure quartz are used in immense quantities for making glass. Another use is as an abrasive, either as sandpaper or as sand or a fine powder. In these forms it is used for dressing stone, wood and leather; while the powder, mixed with soap, forms a widely adver tised cleansing compound. See MINERAL PRO