Quartz is one of the most abundant minerals in the Earth’s crust, second only to feldspar and ahead of mica and all others. It is chemically composed of silica or silicon dioxide. With a rating of 7 on the Mohr’s hardness scale, this mineral is rather hard and possesses a vitreous luster. Quartz forms hexagonal, prismatic crystals when crystallization occurs within open cavities in rocks, whereas in closed spaces small, roundish crystals of quartz are formed instead. Quartz is an extremely durable substance, highly resistant to both physical and chemical weathering. Quartz may contain various impurities resulting in different varieties of this mineral. Pink-colored quartz is referred to as "rose quartz", "citrine" is a yellow- or orange-colored type of quartz, "amethyst" is a purple quartz, "smoky quartz" is grey to black in color, while "milky quartz" is white in color.
Quartz, as one of the most abundant minerals found on the surface of the Earth, has deposits widely distributed across all continents. This durable mineral occurs in all types of rocks, including igneous, metamorphic, and sedimentary deposits. Mountaintops contain quartz as their dominant minerals, while beaches, rivers, and deserts have quartz sands as the primary constituent of their own land surfaces. Even though quartz is a widely occurring mineral, quartz crystals of high purity are, however, rarely found. The Spruce Pine Gem Mine in North Carolina, U.S.A., is one of the few locations in the world where highly pure quartz is mined. Itapore, Goiaz in Brazil, meanwhile, is famous for the discovery of the largest known quartz crystal there, weighing in at more than 44 tons.
Macro-crystalline quartz is usually either already present, or develops together with other minerals during rock formation. The formation of quartz can take place in different types of geological environments. Macrocrystalline quartz formation might occur during cooling and solidification processes of silica-rich molten rock, during the differentiation of pegmatite minerals, or the crystals might otherwise develop from watery solutions of silica when subjected to the right conditions. Finer quartz crystals are, however, formed as a secondary product, and might also occur in rocks initially devoid of silica, like basalt. Individual crystals of quartz grow gradually with the addition of layer by layer of quartz molecules to their respective surfaces.
Quartz sand is extensively used in the glassmaking industry to make different types of glass, such as fiberglass, flat plate, and container glass. The hardness of quartz makes it an extremely suitable material for use as an abrasive. It is thus used in sand blasting, grinding media, and other related processes. Quartz sand is also used as foundry sand for preparing the molds and cores of foundry work. This substance is also used in the petroleum industry in sand slurries for hydraulic fracturing processes, as well as in the rubber and paint manufacture industries as a filler. The railroad and mining industries also utilize quartz sands for traction purposes. Quartz crystals are used in sophisticated electronic equipments like cell phones, watches, and television sets. Amethyst and rose quartz are especially prized quartz varieties which are used as semi-precious gemstones.
Quartz deposits are found in many countries across the world. Arkansas, in the United States, and Brazil are the largest producers of natural quartz in the world. Natural quartz crystals are usually accompanied by a high degree of physical and chemical impurities, and as such require extensive processing in order to produce elecronics-grade quartz. Hence, high-grade quartz crystals are often manufactured in laboratories, and are referred to as ‘cultured quartz’. 'Lascas' are seed crystals required for the growth of cultured quartz. Lascas are imported by the United States from such foreign countries as Brazil, Canada, and Germany. Quartz lascas are also produced by China, Venezuela, and South Africa.