Quartz

Quartz is a hard, crystalline mineral composed of silicon and oxygen atoms. The chemical formula is SiO2.May occur either in well-formed crystals, sometimes enormous and weighing up to 130 kg ( 289 lb), or in compact and concretionary masses, microcrystalline (quartzites) to cryptocrystalline ( agates, jaspers, carnelian, etc.). Colorless when pure (rock crystal). The presence of impurities may give a whole range of colors. Quartz crystals are usually hexagonal and prismatic. Quartz is one of the commonest minerals of the earth's crust. It occurs in plutonic rocks ( granites, granodiorites, tonalites) and in hypabyssal ( granite, porphyries, pegmatites, ect.) and volcanic rocks (quartz porphyry, rhyolites)Stable in sedimentary conditions either either as detrital mineral ( alluvial, marine and desert sands).Quartz is so common that it is impossible to list all the places where it is found.Rock Cystal occurs mainly in pegmatites, Alpine fissures and geodes. Famous localities include Minas Gerais ( Brazil), Val Cristillina in St. Gotthard region, Italy ( Dosso dei Cristalli, Val Malenco, Sondrio, Val d'Aosta, Alto Adige), Austria, France and Japan. Carrara marble from Italy contains unusually clear crystals. Small, perfect rock crystals are sometimes found in cavities in dolomitic rock (Selvino, Bergamo, Italy, Herkimer County NY USA). Collectors of crystals used to believe that transparent, colorless rock crystal war petrified ice. A very important mineral in industry because of its piezoelectric properties, its ability to rotate the plane of polarization of light and its transparency I ultraviolet rays (heat-ray lamps, prisms and lenses)