Black Obsidian

Obsidian is an igneous rock, a mix of cryptocrystalline grains of silica minerals in a glass-like suspension. It is a natural occurrence of volcanic glass created when lava from a volcano cools rapidly with minimal crystal growth. 

Since Obsidian is a natural glass, if in it's raw, unpolished form, it may have razor-sharp edges that can easily cut skin and flesh if broken. Handle with care. Do not grind dry since long-term exposure to finely ground powder may lead to silicosis.