Aquamarine engagement rings? Absolutely! Diamonds may be a girl's best friend, but Aquamarine engagement rings are a unique, original, and a far more affordable choice. A long time favorite of jewelry designers, aquamarine is the birthstone of March. The diamond-like brilliance of an aquamarine ring is sure to attract attention. 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.