Opal engagement rings? Absolutely! Diamonds may be a girl's best friend, but Opal engagement rings are a unique, original, and a far more affordable choice. 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. Once considered more valuable than diamonds, a peridot ring is a must have. This "gem of the sun" is the birthstone of August and is a beautiful match for the lush green tapestry of late summer.