Rainbow Obsidian Faceted BiCone Marquise Straight Drilled beads have a vitreous luster with a well faceted symmetrical 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 exhibit a rainbow hued internal iridescence caused by the high heat formation process. These beads are perfectly matched for color, quality and tone on the very dark green opaque hued bodies with rainbow iridescence that shifts as refracted light enters the stones. Wonderful!