Three birthstones associated with December are: Tanzanite, Turquoise and Blue Topaz. Tanzanite was discovered in the late 1960's in Tanzania and is found exclusively there. Tanzanite exhibits a rich violet-blue hue and vivid colour saturation. Blue Topaz is a more affordable replacement for Tanzanite. Naturally occurring Blue Topaz is quite rare and typically other shades of Topaz are heat treated or irradiated to achieve a more desired darker blue.