obsidian

Noun

WordNet 3.0

Noun (1)

  1. acid or granitic glass formed by the rapid cooling of lava without crystallization; usually dark, but transparent in thin pieces
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Webster's Dictionary (GCIDE)

obsidian \ob*sid"i*an\, n. [L. Obsidianus lapis, so named, according to Pliny, after one Obsidius, who discovered it in Ethiopia: cf. F. obsidiane, obsidienne. The later editions of Pliny read Obsianus lapis, and Obsius, instead of Obsidianus lapis, and Obsidius.] (Min.) A kind of glass produced by volcanoes. It is usually of a black color, and opaque, except in thin splinters. [1913 Webster]

Note: In a thin section it often exhibits a fluidal structure, marked by the arrangement of microlites in the lines of the flow of the molten mass. [1913 Webster]

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