Quartzite (redirected from Quartzites)

quartzite, usually metamorphic rock composed of firmly cemented quartz grains. Most often it is white, light gray, yellowish, or light brown, but is sometimes colored blue, green, purple, or black by included minerals. It results from the metamorphism of pure quartz sandstone. It is most easily distinguished from sandstone by the fact that it fractures across its constituent grains of sand, while sandstone fractures along the line of the cementing material between the grains of sand. Although most quartzites are metamorphic, some are sedimentary in origin, resulting from cementation of quartz sandstone by groundwater solutions containing pure quartz.

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quartzite

Sandstone that has been converted into a solid quartz rock. Quartzites are usually white; they fracture smoothly and break up into rubble under frost action. Sandstone may be converted to quartzite by precipitation of silica from waters below the Earth's surface; such rocks are called orthoquartzites, whereas those produced by recrystallization (metamorphism) are metaquartzites. Because they weather slowly, they tend to project as hills or mountain masses. Many prominent ridges in the Appalachian Mountains are composed of quartzite. Pure quartzites are a source of silica for metallurgical purposes and for the manufacture of silica brick. Quartzite is also quarried for paving and roofing materials.

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quartzite [′kwȯrt‚sīt]

(petrology)

A granoblastic metamorphic rock consisting largely or entirely of quartz; most quartzites are formed by metamorphism of sandstone.

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quartzite

A variety of sandstone composed largely of granular quartz which is cemented by silica forming a homogeneous mass of very high tensile and crushing strengths; esp. used as a building stone, as gravel in road construction, and as an aggregate in concrete.

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Quartzite 

a regionally metamorphosed rock composed mainly of quartz grains that are macroscopically indistinguishable from each other and form a uniform dense mass with a splintery or conchoidal fracture.

In addition to quartz, quartzite often contains other minerals that are used to distinguish special varieties of quartzite; they include mica, garnet, and hornblende. The formation of quartzite is associated with the recrystallization of sandstone in the process of regional metamorphism. Quartzite also includes certain siliceous rocks that are products of the cementation of quartz grains by opal or that are products of the metasomatic replacement of limestone and other calcareous rock by silica. Ferruginous quartzites that, in addition to quartz, contain hematite or magnetite, are formed as a result of the recrystallization of ferruginous sandstones or siliceous schists. Quartzites are characterized by a high SiO₂ content (95–99 percent) and by high refractoriness (up to 1710°-1770°C) and mechanical strength; their compressive strength is 100–455 meganewtons/m² (1,000–4,550 kg/cm²).

Quartzites occur in various metamorphic rocks in the form of solid sheetlike bodies extending for great distances. Quartzites are particularly widely found in Proterozoic deposits. Many varieties of quartzite are valuable minerals. Ferruginous (magnetitic) quartzites are a most important iron ore (for example, the deposits of Krivoi Rog and the Kursk Magnetic Anomaly in the USSR, Lake Superior in the United States, and Labrador in Canada). Quartzites in which the SiO₂ content reaches 98–99 percent are used for manufacturing dinas refractories, for obtaining metallic silicon and its alloys, and as a flux in metallurgy. (Deposits of pure quartzites are found in the Urals, in Karelia, and elsewhere.) Quartzites are also widely used in construction as a decorative stone. (For example, the Lenin Mausoleum and a number of the Moscow subway stations have been faced with the pink-red Shoksha quartzite.) Certain types of quartzite are used as an abrasive material.

REFERENCE

Kurs mestorozhdenii nemetallicheskikh poleznykh iskopaemykh. Edited by P. M. Tatarinov. Moscow, 1969.

A. B. PAVLOVSKII