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.

Related Topics:
Volcanic rock - Lava - Porphyritic - Matrix - Cinder cone - Vesiculated - Intrusive - Phaneritic - Diabase - Gabbro - Ocean - Tectonic plate

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Unweathered basalt is frequently black to greenish-black in color, characterized by a preponderance of calcic plagioclase feldspars and pyroxene together with minor amounts of accessory minerals such as olivine. Basaltic cinders are often red. Glass may be present, particularly as rinds on rapidly chilled surfaces of lava flows, and is commonly (but not exclusively) associated with underwater eruptions. Amygdaloidal structure is common in relic vesicles and beautifully crystallized species of zeolites, quartz or calcite are frequently found.

Related Topics:
Plagioclase - Feldspar - Pyroxene - Mineral - Olivine - Glass - Vesicle - Crystal - Zeolite - Quartz - Calcite

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The lava flows of the Deccan Traps in India, the Columbia River Plateau of Washington and Oregon states in the United States, as well as the Triassic lavas of eastern North America are basalts. Perhaps the most famous basalt flow in the world is the Giant's Causeway on the northern coast of Ireland, in which the vertical joints form hexagonal columns and give the impression of having been artificially constructed.

Related Topics:
Lava - Deccan Traps - India - Columbia River Plateau - Washington - Oregon - United States - Triassic - North America - Giant's Causeway - Ireland - Hexagonal

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Pliny used the word basalt and it is said to have had an Ethiopian origin, meaning a black stone.

Related Topics:
Pliny - Ethiopia

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