Sand
Sand is an example of a class of materials called
granular matter. Sand is a naturally occurring, finely divided
rock, comprising particles or granules ranging in size from 0.0625 (or 1/16) 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 below 0.0625 mm down to 0.004 mm in size. The next larger size class above sand is
gravel, with particles ranging from 2 mm up to 64 mm (see
grain size for standards in use). Sand feels gritty when rubbed between the fingers (silt feels like flour).
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Sand under a scanning electron microscope |
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Close up of black volcanic sand |
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 considerable 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 contain
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, of the like. In most
deserts, sand is a dominant constituent of the soil.
The study of sand is called
arenology. Study of individual grains can reveal quite a bit of historical information as to the origin, kind of transport, etc 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
erosion transported long distances by water or wind will be rounded, with characteristic abrasion patterns on the surface of the grains.
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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.
*
Brick manufacturing plants use sand as an additive with a mixture of
clay and other materials for manufacturing bricks. 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 and are often preferred for intensive
dairy farming because of their excellent drainage characteristics.
*Sand is used in
landscaping, it is added to make small hills and slopes (e.g. for making
golf courses).
*It is the principal component in
glass manufacturing.
*It is often transported to popular beaches where seasonal tides sweep its original sand under the sea.
*
Sandbags are used for protection against
floods and
gun fire. 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.
While sand is generally harmless, one must take care with some activities involving sand such as
sandblasting. 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. There have been a number of lawsuits in recent years where workers have sought damages after they developed
silicosis, a
lung disease caused by inhalation of fine silica particles over long periods of time.
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.
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.
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Quicksand*
Dry quicksand*
Grain size*
Sandstone*
Sandstorm*
Singing sand*
White Sands National Monument*
Falling Sand Game
