Mining is the extraction of valuable minerals or other geological materials from the Earth. This includes metals, coal, gemstones, potash and clay but can also include oil and natural gas. Mining methods often require huge amounts of water to extract the minerals from the ore and this produces washings and slurry. When some minerals are exposed to water they dissolve and create acidic washings which can damage metal pipes. Plastic pipes are more inert to these acidic washings so are often used in preference. Pipe diameters range widely in mining from small diameters supplying potable water to work huts through to three metre pipes carrying slurry to settlement pools.