obsidian
nounA usually black or banded, hard volcanic glass that displays shiny, curved surfaces when fractured and is formed by rapid cooling of lava.
nounA volcanic rock, in a vitreous condition, and closely resembling ordinary bottle-glass in appearance and texture.
nounA kind of glass produced by volcanoes. It is usually of a black color, and opaque, except in thin splinters.
nouna type of black
acid or granitic glass formed by the rapid cooling of lava without crystallization; usually dark, but transparent in thin pieces
