Volcanic tears.Obsidian well be classified as a "volcanic glass" and called "natural glass" is a volcanic lava, being worldwide, mainly near the places of recent or ancient volcanic activity. Pure are colorless, but usually contain inclusions that provides color and optical effects to as a "cat's eye" (golden obsidian) stoned in the right direction. (read more:http://imjoyeria.blogspot.com.co/2014/08/obsidiana.html