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.
Volcanic rock Volcanic rock is an igneous rock of volcanic origin. Volcanic rocks are usually fine-grained or aphanitic to glassy in texture. They often contain ... >
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Igneous rock Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive ... >
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Mid-ocean ridge A mid-ocean ridge or mid-oceanic ridge is an underwater mountain range, formed by plate tectonics. This uplifting of the ocean floor occurs when ... >
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Pumice Pumice is a highly vesicular pyroclastic igneous rock of intermediate to siliceous magmas including rhyolite, trachyte and phonolite. Pumice is ... >
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Crust (geology) In geology, a crust is the outermost layer of a planet.
The crust of the Earth is composed of a great variety of igneous, metamorphic, and ... >
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Mantle plume A mantle plume is an upwelling of abnormally hot rock within the Earth's mantle. As the heads of mantle plumes can partly melt when they reach ... >
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Stratovolcano A stratovolcano is a tall, conical volcano composed of one layer of hardened lava, tephra, and volcanic ash. These volcanoes are characterized by a ... >
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Supervolcano A supervolcano refers to a volcano that produces the largest and most voluminous kinds of eruption on Earth. The actual explosivity of these ... >
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Metamorphic rock Metamorphic rock is the result of the transformation of a pre-existing rock type, the protolith, in a process called metamorphism, which means ... >
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Yellowstone Caldera The Yellowstone Caldera, sometimes known as the Yellowstone supervolcano, is a volcanically active region in Yellowstone National Park. It measures ... >
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