London Topaz engagement rings? Absolutely! Diamonds may be a girl's best friend, but London Topaz engagement rings are a unique, original, and a far more affordable choice. The birthstone of December, the intense deep blue color of a london blue topaz ring can evoke thoughts of warm Caribbean nights. The birthstone of May, an emerald ring symbolizes the eternally returning spring. The velvety green color of emerald is a perfect match for spring and summer fashions.