Luster describes the way light reflects off the surfaces of gemstones. Minerals with high refractive index and can reflect lights well are said to have “adamantine luster,” such as diamond, zircon and rutile; most gem minerals have glassy or “vitreous” luster, such as corundum, emerald, aquamarine, chrysoberyl, quartz, topaz, feldspar, and tourmaline. Sometimes special types of luster develop due to lights interact with elements of gemstones such as internal arrangements, color and smoothness of surfaces, such as the “pearl luster” on pearls and opals; minerals like peridot, jadeite and nephrite have “greasy, fat like luster”; opaque minerals such as turquoise and lapis lazuli exhibits “waxy luster”.