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.

On the Modoc National Forest, obsidian excavation may be done under a Free Use Authorization at any of the four designated mines. Excavation is allowed at these locations only. The Free Use Authorization allows a visitor to collect a predetermined amount per year of obsidian for their own personal use.(This rock had marvelous stripes of rich, vibrant color. photo: Scott's Rock & Gem)