Basalt:
A dark-colored fine-grained extrusive igneous rock composed largely of plagioclase feldspar and pyroxene. Similar in composition to gabbro. Basalt is thought to be one of the main components of oceanic crust.
Base Flow: ...
basalt -- Highly mafic igneous volcanic rock, typically fine-grained and dark in color; rough volcanic equivalent of gabbro.
basalt A dark colored extrusive igneous rock composed chiefly of calcium plagioclase and pyroxene. Extrusive equivalent of gabbro, underlies the ocean
basins and comprises oceanic crust.
Basaltic lava flows often display columnar jointing as a result of contraction forces causing cracks as the lava cools. The extensive crack networks that develop often produce hexagonal columns of lava.
Basalt flows often build up thick individual units. These may be separated by volcanic ash deposits.
Plateau Basalt An accumulation of horizontal flows of basaltic lava. Also called flood basalts.
Partial melting within the mantle of the Moon gave rise to the eruption of mare basalts on the lunar surface.
Lunar maria are vast basaltic plains on the Moon that were thought to be bodies of water by early astronomers, who referred to them as "seas."
Liquid water is thought to be present under the surface of several moons, most notably Europa.
 See also: Surface, Area, Region, Image, Cover
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