Sand

Patterns in the sand

Sand is an example of a class of materials called granular matter.

Sand is a naturally occurring, finely divided rock, made up of particles or granules ranging in size from 0.0625 (or 1/16) to 2 millimeters (mm) in diameter. Each particle in this size range is called a sand grain. Geological material in the next smaller size class is silt, consisting of particles below 0.0625 mm down to 0.004 mm. Material in the size class just above sand is gravel, with particles ranging from 2 mm up to 64 mm. Sand feels gritty when rubbed between the fingers, while silt feels like flour.

Constituents of sand

Sand under a scanning electron microscope

Close up of black volcanic sand

The composition of sand varies according to local rock sources and conditions. In inland continental settings and non-tropical coastal settings, the most common constituent of sand is silica (silicon dioxide), usually in the form of quartz. Given its chemical inertness and considerable hardness, silica is quite resistant to weathering.

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, derived from the weathering and erosion of a nearby granite.

Some locations have sands that contain magnetite, chlorite, glauconite or gypsum. Sands rich in magnetite are dark gray to black in color, as are sands derived from volcanic basalts. The chlorite-glauconite bearing sands are typically green, as are sands derived from basalts (made from 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.

Transport

Sand is transported by wind or water and deposited in various forms, such as beaches, dunes, sand spits, and sand bars. In most deserts, sand is the dominant constituent of the soil.

Study of sand

The study of sand is called arenology. The study of individual grains can reveal quite a bit of historical information about the origin, type of transport, and so forth of the grain. Quartz sand that is recently weathered from granite or gneiss quartz crystals will be angular. It is called sharp sand in the building trade, where it is preferred for concrete mixing, and in gardening, where it is used as a soil amendment to loosen clay soils. Sand that is transported long distances through erosion by water or wind will be rounded, with characteristic abrasion patterns on the surface of the grains.

Uses of sand

Sand sorting tower at a gravel extraction pit.

• Sand is often a principal component of the aggregate used in the preparation of concrete. Sand manufactured at rock crusher plants for use as an aggregate is called mansand. Graded sand is used as an abrasive in sandblasting and is also used in media filters for filtering water.

• In the manufacture of bricks, sand is used as an additive with a mixture of clay and other materials. Sand is also sometimes mixed with paint to create a textured finish for walls and ceilings, or a non-slip surface.

• Sandy soils are ideal for certain crops such as watermelons, peaches, and peanuts. In addition, these soils are often preferred for intensive dairy farming because of their excellent drainage characteristics.

• In landscaping, sand is added to make small hills and slopes, such as for making golf courses.

• Sand is the principal component used in glass manufacturing.

• It is often transported to popular beaches where seasonal tides may sweep the original sand into the sea.

• Sandbags are used for protection against flooding and gunfire. They can be easily transported when empty, and filled with local sand.

• Sand castle building is a popular activity and there are even competitive sand castle building competitions. (See sand art and play for details.)

Hazards of sand

While sand is generally harmless, one must be careful when engaging in some activities with sand such as sandblasting. Based on this, bags of silica sand now typically carry labels warning the user to wear respiratory protection and avoid breathing the fine silica dust because of this. In recent years, workers have filed a number of lawsuits seeking damages after they developed silicosis, a lung disease caused by inhalation of fine silica particles over long periods of time. The "material safety data sheets" (MSDS) for silica sand state that "excessive inhalation of crystalline silica is a serious health concern" [1].

Sand 'mining'

People have been severely injured and even killed after digging sand "caves" in large dunes, sandhills, or even on beaches, when the cave or tunnel collapsed upon them.

Sand in culture and religion

In the Bible, in Genesis 22:17, God states to Abraham:

I will surely bless you and make your descendants as numerous as the stars in the sky and as the sand on the seashore.

See also

• Quicksand
• Dry quicksand
• Grain size
• Sandstone
• Sandstorm
• Singing sand
• White Sands National Monument
• Falling Sand Game

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