Crystalline silica has a higher melting point (1610 °C) than iron, copper or aluminium and other common metals. This enables castings to be made by pouring molten metal into moulds made from silica sand and a binder. The physical and chemical characterisics of the sand are important. In the past naturally clay bonded moulding sands were used. Today mainly clean sands are used with a binding agent added. The sands must have uniform grain size distribution and be generally rounded.

Sales of foundry sand have decreased in recent years due to the demise of the engineering in the UK. About 11% of the sand sold in 2004 was used for foundry purposes.

Foundary moulds are mostly made from a mixture of silica sand, bentonite and water. Much of this material is now recycled for reuse. Spent foundary sand is also used as asphalt filler and in concrete manufacture.