Obsidian (Rainbow)

About Obsidian (Rainbow)

Volcanic glass that displays rainbow-like iridescence caused by nanoscale inclusions of magnetite. The effect shows concentric rings of color when the stone is rotated. It was used for tools and weapons for 700,000+ years - some of the earliest known human artifacts are obsidian. The Aztecs made mirrors from it. It forms when lava cools so rapidly that crystals cannot form. Mexico produces the finest rainbow obsidian. It is used in lapidary for cabochons and carvings. It fractures with conchoidal (shell-like) breaks, creating edges sharper than surgical steel. It has been used in modern surgical scalpels.