quartzite

Quartzite

Quartzite (from German Quarzit^[1]) is a hard metamorphic rock which was originally sandstone.^[2] 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, such as yellow and orange, are due to other mineral impurities.

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. The term is often misused, and should be used for only tightly-cemented metamorphic quartzites, not quartz-cemented quartz arenites^[3]. The typical distinction between the two (since each is a gradation into the other) is a proper quartzite is so highly cemented, diagentically altered, and metamorphosed that it will fracture and break across grain boundaries, not around them.

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

Abandoned quartzite mine in Kakwa Provincial Park, British Columbia, Canada

Quartzite is a decorative stone and may be used to cover walls, as roofing tiles, as flooring, and stair steps. Crushed quartzite is sometimes used in road construction and for railway ballast.^[2] High purity quartzite is used to produce ferrosilicon, industrial silica sand, silicon metal and silicon carbide.^[4]

Occurrences

In the United States, formations of quartzite can be found in some parts of Pennsylvania, eastern South Dakota, Central Texas,^[5] southwest Minnesota,^[6] Devil's Lake State Park in the Baraboo Hills in Wisconsin,^[7] the Wasatch Range in Utah,^[8] near Salt Lake City, Utah and as resistant ridges in the Appalachians^[9] and other mountain regions. Quartzite is also found in the Morenci Copper Mine in Arizona.^[10] The town of Quartzsite in western Arizona derives its name from the quartzites in the nearby mountains in both Arizona and Southeastern California. A glassy vitreous quartzite has been described from the Belt Supergroup in the Coeur d’Alene district of northern Idaho.^[11]

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 6 km north-west of the Long Mynd in south Shropshire. Holyhead mountain and most of Holy island off Anglesey sport excellent Quartzite crags and cliffs. In the Scottish Highlands, several mountains composed of quartzite can be found in the far north-west Moine Thrust Belt (e.g. Foinaven, Arkle)

In Canada, the La Cloche Mountains in Ontario are composed primarily of white quartzite.

References

1. ^ German Loan Words in English
2. ^ ^{a b} Powell, Darryl. "Quartzite". Mineral Information Institute. http://www.mii.org/Minerals/photoquartzite.html. Retrieved 2009-09-09. 
3. ^ Ireland, H. A., 1974, Query: Orthoquartzite????, Journal of Sedimentary Petrology, vol. 44, no. 1, pg. 264-265
4. ^ Krukowski, Stanley T. (2006). "Specialty Silica Materials". in Jessica Elzea Kogel, Nikhil C. Trivedi, James M. Barker, Stanley T. Krukowski. Industrial minerals & rocks: commodities, markets, and uses (7 ed.). Society for Mining, Metallurgy, and Exploration (U.S.). pp. 842. ISBN 0873352335, 9780873352338. http://books.google.com/books?id=zNicdkuulE4C&pg=PA842. 
5. ^ http://www.state.sd.us/DENR/DES/Mining/2002stat.pdf
6. ^ Natural history - Minnesota's geology - SNAs: Minnesota DNR
7. ^ Geology by Lightplane
8. ^ John W Gottman, Wasatch quartzite: A guide to climbing in the Wasatch Mountains, Wasatch Mountain Club (1979) ISBN 0915272237
9. ^ Quartzite
10. ^ Kennedy, B. A. (ed.). Surface Mining, Chapter 9.4: Case Studies: Morenci/Metcalf Society for Mining, Metallurgy, and Exploration, Undated Accessed May 28, 2007
11. ^ White, B.G. and Winston, D., 1982, The Revett/St Regis “transition zone” near the Bunker Hill mine, Coeur d’Alene district, Idaho: Idaho Bureau of Mines and Geology Bulletin 24

External links

• R. V. Dietrich's GemRocks: Quartzite
• CSU Pomona Geology: Quartzite
• Cowen's "The First Geologists" (chapter on Stone Age/Homo habilis use of quartzite)
• Minnesota Department of Natural Resources : Natural History: Minnesota's geology
• Wisconsin's Baraboo Syncline (map and aerial photos of Baraboo quartzite quarries)
• South Dakota 2002 Mineral Summary: Production, Exploration and Environmental Issues (including 2002 quartzite production)
• Big Sioux River: History of Sioux Falls and Quartzite Photos