Obsidian is volcanic glass formed from molten lava that cooled so quickly that no crystalline structure had time to form inside. It is most often black and very shiny, obsidian can be smoothed and polished into mirrors and cabochons for jewelry use and surgical instruments such as scalpels due to obsidian's ability to retain extremely sharp cutting edges. The illustration at right shows primitive obsidian arrowheads such as the Native Americans used to use.
See Also: Jet, Onyx, Cabochon