obsidian
n.n. a shiny black rock that is actually a type of glass. It forms when lava cools very quickly and is used to make sharp tools or jewelry.
n. a naturally occurring volcanic glass formed by the rapid cooling of lava from a volcanic eruption. It is typically black in color and possesses a smooth, glassy surface.
The ancient people used obsidian to make very sharp knives.
Archaeologists found a shard of obsidian at the site, suggesting that the inhabitants traded with distant volcanic regions.
The polished surface of the obsidian mirror reflected the room with such clarity that it seemed to disappear into the darkness of the stone.
From Latin obsidianus; named after Obsidius, who was, according to Pliny, the Roman who discovered the stone in Aethiopia.