Tanzanite engagement rings? Absolutely! Diamonds may be a girl's best friend, but Tanzanite engagement rings are a unique, original, and a far more affordable choice. Tanzanite is the new birthstone of December and has a unique purple-blue color. A tanzanite ring is one of the newest fashion trends and is a must for any jewelry collection. This birthstone of October has a luminosity and glow that makes an opal the treasure that it really is. The rainbow of colors on a neutral white background makes an opal ring a perfect match for any outfit.