Basalt is a common gray to black volcanic rock.
It is usually fine-grained due to rapid cooling of lava on the Earth's surface.
It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria.
Unweathered basalt is black or gray.
Basalt magmas form by decompression melting of peridotite in the Earth's mantle, a process discussed in the entry for igneous rocks.
The crustal portions of oceanic tectonic plates are comprised predominantly of basalt, produced from upwelling peridotite in the mantle below ocean ridges.
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