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Quartzite is a hard, metamorphic rock which was originally sandstone. Through heating and pressure usually related to tectonic compression within orogenic belts, the original quartz sand grains and quartz silica cement were fused into one. Pure quartzite is usually white to grey. Quartzites often occur in various shades of pink and red due to varying amounts of iron oxide. Other colors are due to impurities of minor amounts of other minerals.Orthoquartzite is a very pure quartz sandstone composed of usually well rounded quartz grains cemented by silica. Orthoquartzite is often 99% SiO2 with only very minor amounts of iron oxide and trace resistant minerals such as zircon, rutile and magnetite. Although few fossils are normally present the original texture and sedimentary structures are preserved.
In true metamorphic quartzite, also called meta-quartzite, the individual quartz grains have recrystalized along with the former cementing material to form an interlocking mosaic of quartz crystals. Minor amounts of former cementing materials, iron oxide, carbonate and clay, are often recrystalized and have migrated under the pressure to form streaks and lenses within the quartzite. Virtually all original textures and structure have usually been erased by the metamorphism.
Quartzite is very resistant to chemical weathering and often forms ridges and resistant hilltops. The nearly pure silica content of the rock provides little to form soil from and therefor the quartzite ridges are often bare or covered only with a very thin soil and little vegetation.
Because of its hardness (about 7 on Mohs' scale of mineral hardness), crushed quartzite is often used as railway ballastBallast may mean: railroad or railway ballast: gravel or cinders forming the track-bed on which sleepers (ties) and track is laid, for proper drainage a ship's ballast: water, sand, rocks, or bricks used to weight it down when it has very little cargo (th. In the United States, formations of quartzite can be found in eastern South DakotaSouth Dakota ( In Detail) (Full size) State nickname: The Mount Rushmore State Other U. States Capital Pierre Largest City Sioux Falls Governor Mike Rounds Area Total Land Water % water Ranked 17th 199,905 kmē 196,735 kmē 3,173 kmē 1. 6% Population Total, southwest MinnesotaMinnesota ( In Detail) (Full size) State nickname: North Star State Other U. States Capital Saint Paul Largest City Minneapolis Governor Tim Pawlenty Area Total Land Water % water Ranked 12th225,365 kmē206,375 kmē18,990 kmē8. 4% Population Total ( 2000) D, and as resistant ridges in the Appalachians and other mountain regions. The town of Quartzite in western ArizonaArizona was the 48th state admitted to the United States and is part of the Southwest United States. It is one of the Four Corners states, south and east of the Colorado River, bordering New Mexico, Utah, Nevada, California and Mexico. Its major cities ar derives its name from the quartzites in the nearby mountains.
Metamorphic rocks
