Quartz--the hard rock

Quartz is the second most plentiful mineral in the world next to feldspar. Quartz is mostly clear coloured, but when impurities occur, it can show colours ranging through purple, pink, red, yellow, black, grey, and brown (and of course, there are other colours, too).

Quartz is a fairly hard mineral, 7.0 on Moh's scale. Quartz sand is used often in glass making and abrasives because it is so hard. As geology.com says, “High quality quartz crystals are single-crystal silica with optical or electronic properties that make them useful for specialty purposes. USGS estimates that about ten billion quartz crystals are used every year. Electronics grade crystals can be used in filters, frequency controls, timers, electronic circuits that become important components in cell phones, watches, clocks, games, television receivers, computers, navigational instruments and other products. Optical-grade crystals can be used as lenses and windows in lasers and other specialized devices. Although some natural quartz crystals are used in these applications, most of these special crystals are now manufactured.”

One kind of quartz, tripoli, is used as follows: “Tripoli is crystalline silica of an extremely fine grain size (less than ten micrometers). Commercial tripoli is a nearly pure silica material that is used for a variety of mild abrasive purposes which include: soaps, toothpastes, metal polishing compounds, jewelry polishing compounds and buffing compounds. Tripoli is also used in brake friction products, fillers in enamel, caulking compounds, plastic, paint, rubber and refractories.” (geology.com)

Quartz is used in mining. Because it is so durable, often it is used in petroleum mining. “Quartz sand has a high resistance to being crushed. In the petroleum industry sandy slurries are forced down oil and gas wells under very high pressures. This high pressure fractures the reservoir rocks and the sandy slurry injects into the fractures. The durable sand grains hold the fractures open after the pressure is released. These open fractures facilitate the flow of natural gas into the well bore.” (geology.com)

Quartz is found in many places around the world, since the amount is abundant. “Extraordinarily common. Fine specimens from many places in the Alps of Switzerland and Austria. At Carrara, Tuscany, Italy. From Bourg d'Oisans, Iseµre, France. At Mursinka, Ural Mountains, in the Dodo mine, about 100 km west-northwest of Saranpaul, Subpolar Ural Mountains, and elsewhere in Russia. From Sakangyi, Katha district, Myanmar (Burma). Large twins from Yamanashi Prefecture and many other places in Japan. At Tamboholehehibe and elsewhere in Madagascar. From Brazil, in large amounts from many localities in Rio Grande do Sul, Minas Gerais, Goiás, and Bahia. Around Artigas, Uruguay. At Thunder Bay, Lake Superior, Ontario, Canada. In the USA, from Mt. Ida to Hot Springs, Ouachita Mountains, Arkansas; at Middleville, Herkimer Co., New York; in North Carolina, especially in Alexander and Lincoln Cos. From the Pala and Mesa Grande districts, San Diego Co., California; the El Capitan Mountains, Lincoln Co., New Mexico; the Crystal Park area, Beaverhead Co., and Little Pipestone Creek, Jeferson Co., Montana; and in the Pikes Peak area, El Paso Co., Colorado. From Mexico, in Veracruz and Guerrero.[1]”

http://en.wikipedia.org/wiki/Quartz
http://geology.com/minerals/quartz.shtml
http://rruff.geo.arizona.edu/doclib/hom/quartz.pdf

[1] Quote from: http://rruff.geo.arizona.edu/doclib/hom/quartz.pdf