Obsidian, also known as Dragon Glass (especially with Game of Thrones fans) is produced when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. It is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where the chemical composition (high silica content) causes a high viscosity. Upon rapid cooling it forms a natural glass from the lava. The inhibition of atomic diffusion through this highly viscous lava explains the lack of crystal growth.
Obsidian is hard, brittle, and amorphous; it therefore fractures with very sharp edges. Snowflake obsidian is formed through the inclusion of cristobalite crystals.
Sent as a polished stone appox 2.5 to 3.5cm similar to the one pictured.