Obsidian forms when lava cools quickly. When lava cools more slowly, crystals begin to form, giving the rock a more textured appearance. Snowflake obsidian can form underground, in cracks that the magma seeps into, or above ground in slow-moving, silica-rich lava flows.
Snowflake obsidian forms in areas of past or present volcanic activity. These areas lie along the tectonic plate boundaries. It is found in many areas of the world where volcanic activity has taken place. In the United States, it is found on the West Coast, an area with high levels of tectonic activity.