Onyx engagement rings? Absolutely! Diamonds may be a girl's best friend, but Onyx engagement rings are a unique, original, and a far more affordable choice. Black and gold make a beautiful and elegant combination. A black onyx ring is a perfect accessory for any outfit. 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.