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. Brown gemstones are gaining in popularity and smoky quartz is an affordable choice. A smoky quartz ring goes well with autumn colors and evening wear.