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. Sapphire is the birthstone of September, and pink sapphire is a very popular gemstone in jewelry today. The bright and happy color of a pink sapphire ring is both playful and trendy.