Adamantine luster is the brilliant luster for diamonds and other gemstones. The sparkle originates from the slow speed of light through the mineral and the way it is bent as it passes through. Diamond cuts are angled to take advantage of this and focus and emphasize the light rays still more. Vitreous, or glassy, lusters do not bend or slow the light as much, producing a shiny, but not spectacular, gleam. A resinous luster has the appearance of broken shellac and is due to a further slowing of the light.
Greasy lusters are due to the light interacting with a surface film on the mineral.
A good example is halite, which usually has a film of absorbed water on its surface. Pearly lusters occur when light is split into its different colors by layers below the minerals surface, acting as natural prisms. Some minerals such as clay have a dull or earthy luster. These minerals consist of masses of tiny, randomly oriented particles that scatter the light. Instead of absorbing the light or reflecting it back at a particular angle, each grain reflects some of the light back in a different direction.