When one thinks of an engagement ring, the gemstone that pops up in mind is a diamond. However, there are other gemstones that people have come to appreciate, as they adapt to bolder colours. These gemstones are emerald, ruby, and sapphire. Among the other gemstones, the sapphire is growing in popularity as an alternative to diamond, or as a combination with diamond. The sapphire engagement ring has grown in popularity because of Kate Middleton, who wears a 12-carat royal blue sapphire ring.