Lustre is a term used in mineralogy to describe the appearance of a mineral surface in terms of its light-reflective qualities. It is a physical property used by mineralogists to help identify minerals. Lustre depends upon a minerals refractive power, diaphaneity (degree of transparency), and structure. Variations in these properties produce different kinds of lustre, whereas variations in the quantity of reflected light produce different intensities of the same lustre. There are several kinds of lustre, including:

• Metallic: The lustre of metals, such as gold, tin, and copper. Minerals with a metallic lustre are usually opaque and have refractive indices near 2.5).

• Adamantine: The nearly metallic lustre of diamond and other transparent or translucent minerals with high refractive indices (between 1.9 and 2.5) and relatively great density, such as cerussite and other compounds of lead.

• Vitreous: The lustre of broken glass, which is the most common lustre in the mineral kingdom. It occurs in translucent and transparent minerals with refractive indices between 1.3 and 1.8, such as quartz).

• Resinous: The lustre of yellow resins, such as sphalerite.

• Greasy: The lustre of oiled surfaces, such as nepheline and cerargyrite. Minerals with a greasy lustre often resemble fat or grease and feel greasy to the touch. They contain a great abundance of microscopic inclusions).

• Pearly: The lustre of pearl or mother-of-pearl, such as mica).

Lustre varies over a wide continuum, and there are no rigid boundaries between the different types of lustre. The terms are frequently combined to describe intermediate types of lustre, such as a "vitreous greasy" lustre). Sometimes, lustre can be used to identify minerals. Only certain minerals ever have a pearly, waxy, or greasy lustre. For example, a diamond crystal has a brilliantly shiny adamantine lustre.