Blue Topaz engagement rings? Absolutely! Diamonds may be a girl's best friend, but Blue Topaz engagement rings are a unique, original, and a far more affordable choice. The birthstone of December, the tranquil azure color of a blue topaz ring can evoke thoughts of warm Caribbean seas on a cold winter day. 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.