12 Facts About Basalt

Basalt is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon.

Basalt is an important rock type on other planetary bodies in the Solar System.

Basalt is usually dark grey to black in colour, due to its high content of augite or other dark-coloured pyroxene minerals, but can exhibit a wide range of shading.

Basalt is often porphyritic, containing larger crystals formed prior to the extrusion that brought the magma to the surface, embedded in a finer-grained matrix.

Basalt often contains vesicles, formed when dissolved gases bubble out of the magma as it decompresses during its approach to the surface, and the erupted lava then solidifies before the gases can escape.

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Basalt is produced in subduction zones, where mantle rock rises into a mantle wedge above the descending slab.

Basalt has a lower total content of alkali oxides than trachybasalt and most basanites and tephrites.

Basalt that erupts under open air forms three distinct types of lava or volcanic deposits: scoria; ash or cinder (breccia); and lava flows.

Basalt is the rock most typical of large igneous provinces.

Basalt is common around volcanic arcs, specially those on thin crust.

Basalt commonly erupts on Io, and has formed on the Moon, Mars, Venus, and the asteroid Vesta.

Basalt is a common rock on the surface of Mars, as determined by data sent back from the planet's surface, and by Martian meteorites.