Web Guide: Encyclopedia

Basalt

Basalt is a intrusive or extrusive igneous rock, sometimes porphyritic[?], which can be both fine-grained or dense. The oceanic tectonic plates are predominantly made of basalt.

Basalt is 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. Glass may be present. Amygdaloidal structure is common in such cavities and beautifully crystallized species of zeolites, quartz or calcite are frequently found.

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The lava flows of the Deccan Traps in India, the Columbia 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 Giants Causeway[?] on the northern coast of Ireland, in which the vertical joints form hexagonal columns and give the impression of having been artificially constructed. Pliny used the word basalt and it is said to have had an Ethiopian origin, meaning a black stone.

See also: List of minerals

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