This corresponds to all particles with sizes between coarse sand and cobbles. The Udden-Wentworth scale, widely used by geologists in the US, defines granular gravel as particles with a size from 2 to 4 mm (0.079 to 0.157 in) and pebble gravel as particles with a size from 4 to 64 mm (0.16 to 2.52 in). Gravel is sometimes distinguished from rubble, which is loose rock particles in the same size range but angular in shape.

Many geologists define gravel simply as loose rounded rock particles over 2 mm (0.079 in) in diameter, without specifying an upper size limit. The technical definition of gravel varies by region and by area of application. The American construction industry distinguishes between gravel (a natural material) and crushed stone (produced artificially by mechanical crushing of rock.) Sand and gravel separator in a gravel pit in GermanyĬolloquially, the term gravel is often used to describe a mixture of different size pieces of stone mixed with sand and possibly some clay. Much of the rest is used for road construction, either in the road base or as the road surface (with or without asphalt or other binders.) Naturally occurring porous gravel deposits have a high hydraulic conductivity, making them important aquifers. Almost half of all gravel production is used as aggregate for concrete. Gravel is an important commercial product, with a number of applications. One cubic metre of gravel typically weighs about 1,800 kg (or a cubic yard weighs about 3,000 lb). ISO 14688 grades gravels as fine, medium, and coarse, with ranges 2–6.3 mm to 20–63 mm. In the Udden-Wentworth scale gravel is categorized into granular gravel (2–4 mm or 0.079–0.157 in) and pebble gravel (4–64 mm or 0.2–2.5 in). Gravel is classified by particle size range and includes size classes from granule- to boulder-sized fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes it is also produced in large quantities commercially as crushed stone. Gravel / ˈ ɡ r æ v əl/ is a loose aggregation of rock fragments. Gravel (largest fragment in this photo is about 40 mm (1.6 in))

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