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. Pink tourmaline is a birthstone of October, along with opal, and is a truly special gem. The deep rosy color of a pink tourmaline ring will be sure to attract attention.