Obsidian...

Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock. It is produced when felsic lava extruded from a volcano cools without crystal growth. Obsidian is commonly found within the margins of rhyolitic lava flows known as obsidian flows. Areas of Armenia have experienced such rhyolitic eruptions.

Because of its lack of crystal structure, obsidian blade edges can reach almost molecular thinness, leading to its ancient use as projectile points, and its modern use as surgical scalpel blades.

Snowflake obsidian has a more textured appearance. It can form underground, in cracks that the magma seeps into, or above ground in slow-moving, silica-rich lava flows. The spots/markings on snowflake obsidian are called spherulites, and they are composed of needle-shaped cristobalite, a type of quartz. The end result is a beautiful black color with grayish white patterns throughout the surface.