These are lab grown polymer impregnated synthetic opal beads. They are manufactured by the Kyocera Corporation well known for their outstanding quality in synthetic opal material. They are available here in four colors: Fire and Snow, Tiffany Blue, Carnation Pink, and Black Opal. 3mm or 4mm. They are fully drilled. Use this for a spare color for your captive bead ring, or get a bunch and string a bracelet. Synthetic Opal Captive Bead