Gravel is rock that is of a certain particle size range. In geology, gravel is any loose rock that is larger than two millimeters (mm) (about 1/12 an inch) in its longest dimension but no more than 63 millimeters (about 2.5 inches). The natural erosion of larger rocks has led to the formation of many gravel deposits. In addition, gravel is now produced by crushing rocks mechanically.
Gravel is an important commercial product, used in various applications. Many roadways are surfaced with gravel, especially in rural areas where there is little traffic. It may also be used as an aggregate in concrete. Globally, far more roads are surfaced with gravel than with concrete or tarmac. Russia alone has over 400,000 km of gravel-surfaced roads. Gravel is also used for aesthetic purposes, to enhance the appearance of gardens.
- Bank gravel: naturally deposited gravel intermixed with sand or clay found in and next to rivers and streams. Also known as “Bank run” or “River run”.
- Bench gravel: a bed of gravel located on the side of a valley above the present stream bottom, indicating the former location of the stream bed when it was at a higher level.
- Creek rock: this is generally rounded, semi-polished stones, potentially of a wide range of types, that are dredged or scooped from river beds and creek beds. It is also often used as concrete aggregate and less often as a paving surface.
- Crushed stone: rock crushed and graded by screens and then mixed to a blend of stones and fines. It is widely used as a surfacing for roads and driveways, sometimes with tar applied over it. Crushed stone may be made from granite, limestone, dolomite, and other rocks. Also known as “crusher run”, DGA (Dense Grade Aggregate) QP (Quarry Process), and shoulder stone.
- Fine gravel: gravel consisting of particles with a diameter of 2 to 4 mm.
- Lag gravel: a surface accumulation of coarse gravel produced by the removal of finer particles.
- Pay gravel: also known as “pay dirt”; a nickname for gravel with a high concentration of gold and other precious metals. The metals are recovered through gold panning.
- Pea gravel: gravel that consists of small, rounded stones used in concrete surfaces. It is also used for walkways, driveways and as a substrate in home aquariums.
- Piedmont gravel: a coarse gravel carried down from high places by mountain streams and deposited on relatively flat ground, where the water runs more slowly.
- Plateau gravel: a layer of gravel on a plateau or other region above the height at which stream-terrace gravel is usually found.