When the luster of a diamond is mentioned it refers to the way that light interacts with the surface. Luster does not have anything to do with shape or size but is related to transparency, crystal habit, surface conditions and index of refraction.
The index of refraction is something that mineralogists are very interested in. It’s a critical tool in studying and evaluating minerals, including diamonds, notes Galleries.com. The index of refraction is the geometric ratio of the angle at which lights comes to the crystal, which is the angle of incident, and by the angle at which light, called the angle of refraction, is bent as it enters a crystal. High refraction equals good luster.
A diamond has high refraction, is the hardest substance found in nature, and is durable. A diamond is transparent and conducts heats five times more efficiently than silver, which is the second best element. The luster of a diamond is adamantine to waxy and is considered to have a metallic luster. Luster means “light,” and is derived from the Latin word lux. Luster suggests brilliance, gloss or radiance.
Adamantine luster means that the diamond has good transmitting properties and reflects light brilliantly. Adamantine minerals, such as a diamond, possess remarkable luster. Minerals that are adamantine have a high refractive index and are translucent or transparent. Minerals that have relatively high but lesser degrees of luster are called sub-adamantine. An example of this would be a garnet.
Non-metallic luster in a mineral can range from glassy, which is called vitreous, to dull. Diamonds have brilliant or adamantine luster; quartz have vitreous luster, which has the luster of broken glass. Other varieties of luster include pearl, which is pearl-like and iridescent; resinous, which is the luster of resin and silky, which is comparable to a soft light displayed by fibrous material, such as gypsum, and dull or earth, which results when there are finely crystallized minerals.
Luster can unofficially mean many things to those who are in the market for a diamond. It can refer to brightness, radiance, polish, shine, radiance and gloss. Who doesn't love the glorious sparkle of a beautiful diamond?