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Gravel is rock that is of a certain size range. In geology, gravel is any loose rock that is at least two millimeters in its largest dimension (about 1/12 of an inch), and no more than 75 millimeters (about 3 inches). Sometimes gravel is restricted to rock in the 2-4 millimeter range, with pebble being reserved for rock 4-75 millimeters (some say 64 millimeters). The next smaller size class in geology is sand, which is 0.02 mm to 2 mm in size. The next larger size is cobble, which is 75 (64) millimeters to 256 millimeters (about ten inches).

Gravel is an important commercial product, used in many applications. Some important types of gravel include:

In Britain, gravel always refers to smooth, rounded, river-worn material, never to angular stones or crushed rock. British gravel ranges in size from 4 mm to about 30 mm, the smaller sizes up to 8 mm are usually called 'pea gravel'.

Many roadways are surfaced with gravel, especially in rural areas where there is little traffic.

See also