reworked and quartz was the primary mineral that endured heavy weathering. While the majority of quartz crystallizes from molten magma, quartz also chemically precipitates from hot hydrothermal veins as gangue, sometimes with ore minerals like gold, silver and copper. Large crystals of quartz are found in magmatic pegmatites. Well-formed crystals may reach several meters in length and weigh hundreds of kilograms. Elemental impurity incorporation strongly influences the ability to process and utilize quartz. Naturally occurring quartz crystals of extremely high purity, necessary for the crucibles and other equipment used for growing silicon wafers in the semiconductor industry, are expensive and rare. These high-purity quartz are defined containing less than 50 ppm of impurity elements. A major mining location for high purity quartz is the Spruce Pine Gem Mine in Spruce Pine, North Carolina, United States. Quartz may also be found in Caldoveiro Peak, in Asturias, Spain. The largest documented single crystal of quartz was found near Itapore, Goiaz, Brazil; it measured approximately and weighed 39,916 kilograms. Mining Quartz is extracted from open pit mines. Miners occasionally use explosives to expose deep pockets of quartz. More frequently, bulldozers and backhoes are used to remove soil and clay and expose quartz veins, which are then worked using hand tools. Care must be taken to avoid sudden temperature changes that may damage the crystals. Almost all the industrial demand for quartz crystal (used primarily in electronics) is met with synthetic quartz produced by the hydrothermal process. However, synthetic crystals are less prized for use as gemstones. The popularity of crystal healing has increased the demand for natural quartz crystals, which are now often mined in developing countries using primitive mining methods, sometimes involving child labor. Related silica minerals Tridymite and cristobalite are high-temperature polymorphs of SiO2 that occur in high-silica volcanic rocks. Coesite is a denser polymorph of SiO2 found in some meteorite impact sites and in metamorphic rocks formed at pressures greater than those typical of the Earth's crust. Stishovite is a yet denser and higher-pressure polymorph of SiO2 found in some meteorite impact sites. Lechatelierite is an amorphous silica glass SiO2 which is formed by lightning strikes in quartz sand. Safety As quartz is a form of silica, it is a possible cause for concern in various workplaces. Cutting, grinding, chipping, sanding, drilling, and polishing natural and manufactured stone products can release hazardous levels of very small, crystalline silica dust particles