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.”