Basalt

Basalt is a common gray to black volcanic rock. It is usually fine-grained due to rapid crystallization as lava on the Earth's surface. It may be porphyritic containing larger crystals in a fine matrix. Basalt in the tops of subaerial lava flows and cinder cones will often be highly vesiculated, imparting a lightweight "frothy" texture to the rock. The term basalt is at times applied to shallow intrusive rocks with a composition typical of basalt, but rocks of this composition with a phaneritic (coarse) groundmass should generally be referred to as diabase or gabbro. The crustal portions of oceanic tectonic plates are predominantly made of basalt.

Lunar basalt

The dark areas visible on Earth's moon, the lunar mares, are plains of basalt and gabbro, and basalt Moon samples were brought to Earth by the astronauts of the Apollo program.

Related Topics:
Moon - Lunar mare - Astronauts - Apollo program

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