Obsidian is made by the lava that comes from a volcano that rapidly cools into a glass looking igneous rock that lacks any crystal growth. Obsidian is translucent and is black. On the Mohs scale of hardness it is a 5-6. The luster it gives off is vitreous. Back in the day this rock was used for arrowheads or sharp weapons because it could be fractured into sharp objects easily and it was durable. It also was used for early mirrors.
