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Quartzite
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Quartzite (from German Quarzit) is a hard metamorphic rock which was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and red due to varying amounts of iron oxide (Fe2O3).
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Encyclopedia
Quartzite (from German Quarzit) is a hard metamorphic rock which was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and red due to varying amounts of iron oxide (Fe2O3). Other colors are commonly due to impurities of minor amounts of other minerals.
When sandstone is metamorphosed to quartzite, the individual quartz grains recrystallize along with the former cementing material to form an interlocking mosaic of quartz crystals. Most or all of the original texture and sedimentary structures of the sandstone are erased by the metamorphism. Minor amounts of former cementing materials, iron oxide, carbonate and clay, often migrate during recrystallization and metamorphosis. This causes streaks and lenses to form within the quartzite.
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.
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 therefore the quartzite ridges are often bare or covered only with a very thin soil and little vegetation.
Uses
Because of its hardness, about 7 on the Mohs' scale of mineral hardness. crushed quartzite is often used as railway ballast.
Occurrences
In the United States, formations of quartzite can be found in some parts of Pennsylvania, eastern South Dakota, Central Texas, southwest Minnesota, Devil's Lake State Park in the Baraboo Hills in Wisconsin, the Wasatch Range in Utah, near Salt Lake City, Utah and as resistant ridges in the Appalachians and other mountain regions. Quartzite is also found in the Morenci Copper Mine in Arizona. The town of Quartzsite in western Arizona derives its name from the quartzites in the nearby mountains in both Arizona and Southeastern California. In the United Kingdom a craggy ridge of quartzite called the Stiperstones (early Ordovician - Arenig Epoch, 500 Ma) runs parallel with the Pontesford-Linley fault 6km north-west of the Long Mynd in south Shropshire.
The La Cloche Mountains in Ontario are also composed primarily of white quartzite.
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