Sand

Sand is an example of a class of materials called granular matter. Sand is a obviously occurring, finely divided rock, comprising particles or granules ranging in size from 1/16 to 2 millimeters. An individual element in this range size is termed a sand grain. The next smaller size class in geology is silt: particles below 1/16 mm down to 1/256 mm (0.004 mm) in size. The next larger size class above sand is gravel, with particles ranging up to 64 mm The most common constituent of sand in inland continental settings and non-tropical coastal settings is silica (silicon dioxide), usually in the form of quartz which because of its chemical inertness and substantial hardness is quite resistant to weathering. However, the composition of sand varies according to local rock sources and conditions. The bright white sands found in tropical and subtropical coastal settings are ground-up limestone. Arkose is a sand or sandstone with considerable feldspar content which is derived from the weathering and erosion of a usually nearby granite. Some locations have sands that have magnetite, chlorite, glauconite, or gypsum. Sands rich in magnetite are dark to black in color, as are sands derived from volcanic basalts. The chlorite-glauconite bearing sands are typically green in color, as are sands derived from basalts (lavas) with a high olivine content. The gypsum sand dunes of the White Sands National Monument in New Mexico are famous for their bright, white color. Sand deposits in some areas contain garnets and other resistant minerals, including some small gemstones.
Sand is transported by wind or water and deposited in the form of beaches, dunes, sand spits, sand bars, and the like. In most deserts, sand is a dominant constituent of the soil.
The study of sand is called arenology.