Sand is a mixture of very small pieces of different rocks or minerals. Sand grains are between the size of gravel grains (which is from 2 mm to 64 mm) and the size of silt (which is around 0.0625 mm to 0.004 mm). It is found on beaches, and in deserts.
Sand is most of the time made of silica (silicon dioxide, or SiO2). Sand is also formed by Granite by weathering and erosion. Sand is made from large boulders eroding (being broken apart by wind or rocks). They get smaller and smaller until they reach the beach or a low lying area. Sand dunes are made when wind or a river pulls sand into a mountain-like shape. They can be found in deserts, but sometimes high up on beaches too.
Apparently sand can be mixed with water to make concrete this is totally untrue for you would need other materials and/or ingredients. It can also be used to make sand castles. When mixed with water sand will not become mud but the sand would slowly and slyly sink to the bottom of the mixture this is why the sea is not covered in a seawater/sand mixture but has sand on the seabed.
Sand on a beach in Calabria. You can see sand dunes here.
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