Obsidian is a type of black or dark glass formed from cooling lava. So if you find a shiny, hard, dark piece of glass next time you’re hanging around a volcano, it’s probably a piece of obsidian.

The word obsidian essentially means “stone of Obsius.” So who was Obsius? According to an ancient Roman writer, he was the guy who first found this type of stone in Ethiopia. You’ll find obsidian used as a modifier a lot. Think of an obsidian arrowhead, blade or mirror. Sometimes it is used as a fancy way of describing people’s eyes in romance novels as in, “Her eyes were dark and shining, two obsidian orbs.”

Definitions of obsidian

n acid or granitic glass formed by the rapid cooling of lava without crystallization; usually dark, but transparent in thin pieces

Type of:
volcanic glass
a kind of natural glass produced when molten lava cools very rapidly

Sign up, it's free!

Whether you're a student, an educator, or a lifelong learner, Vocabulary.com can put you on the path to systematic vocabulary improvement.