This matching set comes standard with a metal core with a composite matrix of strontium aluminate (what makes the ring glow) and amethyst crystals. The two materials combine to give the center an amazing organic look and feel. The standard transparent amethyst also gives the rings a look of depth that can only be fully appreciated in person, but the inlay can also be among a variety of exotic materials such as meteorite and dinosaur bone. Sizing: For orders placed through Facebook or Instagram Shop, please contact us at support@patrickadairdesigns.com to give us your ring size. We will also reach out to you shortly after you place your order to collect any necessary information.