Like moonstones, opaline and OPALESCENT are both terms used to describe a type of gemstone. Opaline is a term used to describe a gemstone with a milky or pearly luster, while OPALESCENT is used to describe a gemstone with a play of colors that change when viewed from different angles. Both terms are often used to describe the same type of gemstone, but opaline is more commonly used to describe a gemstone with a milky or pearly luster, while OPALESCENT is used to describe a gemstone with a play of colors.