AZTEC SNOWFLAKE OBSIDIAN BEADS

 Obsidian has been used for tool-making since at least 21,000 B.C. and in jewelry for many centuries. American Indians used it for arrowheads, and the Aztecs used a great deal of obsidian for items including sacrificial knives and mirrors. Today, obsidian is used for dating; the stone weathers slowly at a uniform rate, and the thickness of the weathered layer is measured microscopically and gauged against known standards to give a date in years.