AA Quality Rainbow Obsidian Plain Coin Beads have a vitreous luster with a symmetrical, straight drilled shape. These obsidian gems are formed by sand particles which come into contact with extreme heat inside the Earth's crust (volcanic vents) then as they solidify, they exhibit a rainbow hued internal iridescence caused by the high heat formation process. These beads are matched for color, quality and tone on the opaque bodies with rainbow iridescence that shifts as refracted light enters the stones.