How obsidian changes to shale?
Obsidian changes into shale through weathering and compaction. Obsidian, an igneous rock, can get worn down into particles, usually through grind up against other rocks. Those tiny obsidian particles are then carried away by wind or water, and deposited in a river bed or out in the ocean. As time goes on, other sediments are then piled on top of the obsidian particles, compacting them down into shale.
