Sand
![Sand [[dune](https://upload.wikimedia.org/wikipedia/commons/8/8b/Libya_4608_Idehan_Ubari_Dunes_Luca_Galuzzi_2007.jpg)
The composition of sand varies, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal settings is silica (silicon dioxide, or SiO2), usually in the form of quartz.
Calcium carbonate is the second most common type of sand, for example, aragonite, which has mostly been created, over the past 500million years, by various forms of life, like coral and shellfish. For example, it is the primary form of sand apparent in areas where reefs have dominated the ecosystem for millions of years, as in the Caribbean. Somewhat more rarely, sand may be composed of calcium sulfate, such as gypsum and selenite, as is found in places such as White Sands National Park and Salt Plains National Wildlife Refuge in the U.S.
Sand is a non-renewable resource over human timescales, and sand suitable for making concrete is in high demand. Desert sand, although plentiful, is not suitable for concrete. Fifty billion tons of beach sand and fossil sand are used each year for construction. Provided by Wikipedia
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106by Enger, Per S., Kristensen, Leif, Sand, OlavGet access
Published in Comparative Biochemistry and Physiology Part A: Physiology (1976)
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111by Elberling, Bo, Schippers, Axel, Sand, WolfgangGet access
Published in Journal of Contaminant Hydrology (2000)
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117by Ryan, Conor, Papastavrou, Vassili, Sand, Peter H.Get access
Published in Journal of International Wildlife Law & Policy (2021)
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