According to The Mineral and Gemstone Kingdom, cut diamonds have an adamantine luster, a rare and prized luster which is marked by exceptional shininess and brilliance. Raw, uncut diamonds have a more greasy luster.
Minerals with the adamantine luster are extremely rare; only a few other minerals possess comparable sheen. The diamond is considered the superlative example of adamantine, but the luster can be found in other minerals like cubic zirconia. Minerals with similar but slightly duller sheen, like garnet, are known as subadamantine. The greasy luster found in raw diamond ore is more common and can be found in minerals such as opal and chrysocolla.