[uh
b-sid-ee-uhn] 
| a volcanic glass similar in composition to granite, usually dark but transparent in thin pieces, and having a good conchoidal fracture. |
| 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.] |
| obsidian (ŏb-sĭd'ē-ən) Pronunciation Key
A shiny, usually black, volcanic glass. Obsidian forms above ground from lava that is similar in composition to the magma from which granite forms underground, but cools so quickly that minerals do not have a chance to form within it. |