California Rainbow Obsidian Is a Natural Wonder (Amazing Photos)

Obsidian is dense volcanic glass, usually rhyolite in composition and typically black in color. Obsidian with multicolored iridescence caused by inclusions of magnetite nanoparticles. Obsidian is often formed in rhyolite lava flows where the lava cools so fast that crystals do not have time to grow.

Glass, unlike crystals, has no regular structure and therefore fractures in smooth, curved shapes. The intersections of these fractures can form edges sharper than the finest steel blades. For this reason, obsidian was used by many native cultures to make arrowheads and blades. Even today, surgeons use the knife sharp edges in operations.