I could go on but, let’s let the ring do the talking. Handcrafted ring in 18k rose gold with 3.58 ct. cushion spinel, 0.43 ct. t.w. round alexandrite, and 0.13 ct. t.w. brilliant diamonds by Omi Priv é, price on request But while their rarity would logically make them the most precious of minerals, many would not work in a Valentine’s Day ring diamond. In fact, there are many gemstones that are just as beautiful, but much rarer than the diamond. Black Opal The American Gemstone Society adds further options: alexandrite for June Reilly's Auction Rooms in Dublin took place on January 27. The top lot was a diamond solitaire ring with old cut diamond to diamond shoulders, mounted in white gold. .