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About Quartz
Quartz is a semi-precious gemstone composed of silicon dioxide. Because of its simple silicate structure, it is the second most common mineral found in the Earth's crust, after feldspar. Quartz forms when the silicate-rich melt from igneous rocks freezes, or when the element silica is dissolved in hot water then allowed to cool slowly. The latter process creates larger samples of quartz, which comes in many different varieties, including agate, amethyst, citrine, rose quartz, smoky quartz and milk quartz. Quartz generally has a density of about 2.65 grams per cubic centimeter and a hardness of 7 on the Mohs scale.
Clear Quartz
Rock crystal is the name given to all quartz that is clear and colorless in appearance. While other types of quartz have varying degrees of opacity, the primary characteristic of rock crystal is that it is clear and colorless. Besides these qualities, rock crystal shares all the same properties as other types of quartz, including hardness and density. Rock crystal falls between 1.544 and 1.553 on the index of refraction, which measures the speed with which light passes through a substance. Rock crystal also commonly is referred to simply as crystal.
Formation
Rock crystal is formed very much in the same way as other varieties of quartz. However, certain geological conditions encourage the formation of rock crystal as opposed to agate, citrine or other quartz varieties. Though all quartz begins from the same material -- silicate dioxide -- rock crystal must be formed in a slow-changing environment to guarantee that it retains its clear, colorless properties. For instance, the rock-crystal-rich Alpine mountains have rock crystal that has formed over several million years during the slow process of uplifting and folding mountains.
Location
Rock crystal quartz can be found in many places throughout the world. The Alps have been a popular source for the harvesting of rock crystal since the Roman Empire. Additionally, rock crystal is commonly harvested from the Ouachita Mountains in Arkansas, Minas Gerais in Brazil, Polar Ural in Russia, Peru, Nepal and Madagascar.
Uses
Rock crystal is considered a semi-precious gemstone. Because it is clear, colorless abundant and easy to cut, rock crystal commonly is used as a substitute for diamonds. Rock crystal is also used for ornamental carvings and to make crystal balls for fortune tellers. The crystals of chandeliers and other decorative household pieces are frequently carved from pieces of rock crystal.