Natural Black Rectangle Shaped Obsidian Stone Crystal with Black Rope Necklace
Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock and produced when volcano cools rapidly with crystal growth. It is commonly found within the margins of lava flows, where the chemical composition induces a high degree of viscosity and polymerization of the lava. Obsidian is hard and brittle with very sharp edges. In the past it was used to manufacture cutting and piercing tools and it has been used experimentally as surgical scalpel blades.