obsidian
/əbˈsɪdɪən
/noun [mass noun]
A hard, dark, glass-like volcanic rock formed by the rapid solidification of lava without crystallization.Hard stones such as obsidian and rock crystal were added to the repertoire of the stone-vase maker....
- The earliest mirrors were of obsidian, a black volcanic rock that could be carved and polished.
- The presence of basalt and obsidian is a sign of volcanic activity and the instability of the earth's crust in this area.
Origin
Mid 17th century: from Latin obsidianus, error for obsianus, from Obsius, the name (in Pliny) of the discoverer of a similar stone.