Blue Topaz BirthstoneDiamond And Square Ring 10K White Gold10k white gold diamond and square blue topaz birthstone ring. The perfect December birthstone ring or mothers ring, this 10 karat white gold band has square blue topaz and diamonds alternating half way around the ring. All birthstone rings and mother's rings are available in all birthstones, although the April (diamond) version may cost more. Looks great worn alone, or as a stackable ring.