Lustrous gems are precious stones that have a beautiful shine and sparkle. Opals (5 letters) and pearls (6 letters) are two of the most popular examples of lustrous gems. Opals are made up of silica and water, and they come in a variety of colors. Pearls are formed when an irritant gets inside an oyster or mollusk, and they are usually white or cream-colored. Both opals and pearls are highly sought after for their beauty and rarity.