Quartz is our most common mineral. Quartz is made of the two most abundant chemical elements on Earth: oxygen and silicon. Atoms of oxygen and silicon join together as tetrahedrons (three sided pyramids). These stack together to build crystals. Billions of tetrahedrons are needed to build even a small crystal. Quartz is an almost pure chemical compound with constant physical properties.
Quartz makes up about 12 percent of the land surface and about 20 percent of the Earth's crust. Most of the remaining crustal rocks are rich in silicate minerals which include silicon and oxygen together with other elements.
Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2. Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar.
Quartz exists in two forms, the normal α-quartz and the high-temperature β-quartz, both of which are chiral. The transformation from α-quartz to β-quartz takes place abruptly at 573 °C (846 K; 1,063 °F). Since the transformation is accompanied by a significant change in volume, it can easily induce micro fracturing of ceramics or rocks passing through this temperature threshold.
There are many different varieties of quartz, several of which are classified as gemstones. Since antiquity, varieties of quartz have been the most commonly used minerals in the making of jewellery and hardstone carvings, especially in Eurasia.
Quartz is the mineral defining the value of 7 on the Mohs scale of hardness, a qualitative scratch method for determining the hardness of a material to abrasion.
Quartz sand is often blended with cohesive agents such as clay, resin sodium silicate, and oil, and used for the purpose of molding and metal casting. The properties of quartz sand such as high melting point, high strength and refractoriness help in the process of metal casting. Also, microcrystalline quartz is used to smoothen out crude edges on metals after they are cut, cast or drilled.
Quartz sand is also in the metal casting industry, is added to molten metals for the process of removing impurities, mostly oxygen. The sand gets bonded with the impurities and is then easily removed.
Quartz sand is used in the production of refractory bricks because of its sheer strength and resistance to heat. It is also used as a flux to smelt out crude edges on metals after they have been cast, cut or drilled. Due to its hardness (it is harder than most natural minerals), and resistance to corrosion, quartz sand is considered a wonderful abrasive. Also, it is used for sandblasting, glass grinding media, scouring cleansers (powder), and sanding and sawing grit.