Sand is a granular substance made up of small rock and mineral particles that have been coarsely split. Sand comes in a variety of components, but its grain size is what defines it. The granules of sand are smaller than those of gravel and coarser than those of silt. Sand can also refer to a type of soil or a textural class of soil, such as one with more than 85 percent sand-sized particles by mass.

Sand composition varies depending on local rock sources and circumstances, although silica (silicon dioxide, or SiO2), generally in the form of quartz, is the most frequent element of sand in inland continental settings and non-tropical coastal settings.

Calcium carbonate is the second most prevalent type of sand, after aragonite, which was primarily formed by various types of life, such as coral and shellfish, over the last 500 million years. It’s the most common type of sand in places like the Caribbean, where reefs have dominated the environment for millions of years. Sand can also be made up of calcium sulfate minerals like gypsum and selenite, which can be found in areas like White Sands National Park and Salt Plains National Wildlife Refuge in the United States.

Over human timeframes, sand is a nonrenewable resource, and sand suitable for concrete production is in great demand. Despite its abundance, desert sand is unsuitable for concrete. Each year, 50 billion tonnes of beach sand and fossil sand are utilized in buildings.

Sand is defined in a variety of ways. Sand is defined as particles with a dimension of between 0.074 and 4.75 millimeters in the scientific Unified Soil Classification System used in engineering and geology, which correlates to US Standard Sieves. According to another definition, sand particles range in diameter from 0.0625 mm (or 16 mm) with a volume of about 0.00012 cubic millimeters to 2 mm with a volume of approximately 4.2 cubic millimeters, with a volume difference of 34,688 millimeters. A sand grain is any particle that falls within this size range. Sand grains are found between gravel and silt (the latter system has particles ranging from 2 mm to 64 mm, while the former system has particles ranging from 4.75 mm to 75 mm) (particles smaller than 0.0625 mm down to 0.004 mm). The size specification between sand and gravel has stayed consistent for more than a century, although under the Albert Atterberg standard in use throughout the early twentieth century, particle sizes as tiny as 0.02 mm were considered sand. The sand grains in Archimedes’ The Sand Reckoner, published circa 240 BCE, had a diameter of 0.02 mm. The United States Department of Agriculture specified 0.05 mm in 1938. The American Association of State Highway and Transportation Officials established an engineering standard in 1953 that defined the minimum sand size at 0.074 mm. When you touch sand between your fingers, it feels rough. Silt, on the other hand, feels like flour.

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