What is Basalt?
[[File:BasaltUSGOV.jpg|thumb|200px|right|Basalt]] [[File:Giants causeway closeup.jpg|thumb|right|200px|Large masses cool slowly to form a polygonal joint pattern.]] [[File:Sheepeater Cliff, Yellowstone, June 21, 2010.jpg|thumb|right|250px|Columnar basalt in [[Yellowstone National Park]]. See also [[Giant's Causeway]] in [[Northern Ireland]], and [[Fingal's Cave]], [[Inner Hebrides]]]] '''Basalt''' is a common grey to black [[Rock (geology)|rock]]. It is pushed out ([[extrusive|extruded]]) by [[volcanos]]. The [[lava]] is rich in [[magnesium]] and [[iron]]. It has [[olivine]] and [[pyroxene]] minerals which make it dark in colour. Basalt is usually fine-grained because the [[lava]] cools rapidly on the Earth's surface. [[Flood basalt]]s are commonplace, formed by lava pouring out and solidifying. On Earth, most basalt [[magma]]s have formed by the hot molten [[Mantle (geology)|mantle]]. Basalt is a type of intrusive rock meaning it forms inside of the volcano. Basalt has also formed on Earth's [[Moon]], [[Mars]], [[Venus]], and even on the asteroid [[Vesta]]. The crustal portions of [[ocean]]ic [[tectonic plate]]s are made mostly of basalt, produced from upwelling mantle below [[mid-ocean ridge]]s. Unweathered basalt is black or grey. Basalt blocks are often used for roads and pavements (sidewalks), and for houses and other buildings. It is hard-wearing and heat resistant. Basalt can be made into [[fibre]]. Basalt fibre is often used as a safe replacement for [[asbestos]]. Intense heat and pressure can change basalt into its [[metamorphic rock]] equivalent. The rocks known as [[greenstone]] are basalt which has been metamorphised. See [[metamorphic rock]] for more details. {{Rock type}} {{-}} {{sci-stub}} [[Category:Minerals]] [[Category:Igneous rocks]]