a volcanic glass similar in composition to granite, usually dark but transparent in thin pieces, and having a good conchoidal fracture.
Origin: 1350–1400; < L Obsidiānus, printer's error for Obsiānus pertaining to Obsius, the discoverer (according to Pliny) of a similar mineral in Ethiopia; r. ME obsianus < L; see -an
ob·sid·i·an (ŏb-sĭd'ē-ən) n. A usually black or banded, hard volcanic glass that displays shiny, curved surfaces when fractured and is formed by rapid cooling of lava.
[Latin obsidiānus, misreading of obsiānus (lapis), Obsian (stone), obsidian, after Obsius, a Roman who supposedly discovered it or a similar mineral.]