Obsidian
Pronunciation : Ob*sid"i*an
Part of Speech : n.
Etymology : [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.)
Definition : Defn: A kind of glass produced by volcanoes. It is usually of a black color, and opaque, except in thin splinters.
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.
Source : Webster's Unabridged Dictionary, 1913