Coarse aggregates are excavated from natural deposits of gravel or stones and then washed to remove dirt, salts and clay. The term describes materials such as natural gravel, crushed gravel or crushed stone that will not pass through a 5mm sieve. Bigger stones are often crushed to make smaller pieces. Washing, crushing and sieving usually take place in the location of the excavations. A coarse aggregate used for concrete is likely to pass through a 19mm sieve but stay on a 10mm sieve.