Obsidian’s Edge In the Sierra de las Navajas (Razor or Knife mountains), about two hours outside of Lake Chapala, is a modern mine that recently crossed paths with pre-Hispanic tunnels used to quarry obsidian by the Aztecs. Obsidian is a naturally occurring volcanic glass formed into a kind of rock by the rapid cooling of lava. The majority of obsidian is black or gray but a rarer green obsidian was...