Where Does Sand Come From?
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. As the term is used by geologists, sand particles range in diameter from 0.0625 (or 1⁄16 mm) to 2 millimeters. An individual particle in this range size is termed a sand grain. The next smaller size class in geology is silt: particles smaller than 0.0625 mm down to 0.004 mm in diameter. The next larger size class above sand is gravel, with particles ranging from 2 mm up to 64 mm (see particle size for standards in use). Sand feels gritty when rubbed between the fingers (silt, by comparison, feels like flour). Sand is commonly divided into five sub-categories based on size: very fine sand (1/16 – 1/8 mm diameter), fine sand (1/8 mm – 1/4 mm), medium sand (1/4 mm – 1/2 mm), coarse sand (1/2 mm – 1 mm), and very coarse sand (1 mm – 2 mm). These sizes are based on the Φ sediment size scale, where size in Φ = -log base 2 of size in mm.
Grains of sand are really very tiny particles of rock. It takes time and certain kinds of weather to turn rock into sand. Rain, frost, and wind can do the job. At beaches, the tide hitting against the rocks forms sand. Salt water, too, forms sand by dissolving minerals in the rocks. Since rocks are made up of minerals and since
