Lustre (or luster) is a description of the way light interacts with the surface of a crystal, rock, or mineral. The word lustre traces its origins back to the Latin word lux, meaning “light”, and generally implies radiance, gloss, or brilliance.
A range of terms are used to describe lustre. Many terms refer to materials having similar lustres, such as earthy, metallic, greasy, and silky. Similarly, the term vitreous (derived from the Latin for glass, vitrum) refers to a glassy lustre. A list of these terms is given below.
Lustre varies over a wide continuum, and so there are no rigid boundaries between the different terms. (For this reason, different sources can often describe the same mineral differently. This ambiguity is further complicated by the fact that lustre can vary widely within a particular mineral species.) The terms are frequently combined to describe intermediate types of lustre (for example, a “vitreous greasy” lustre).
Some minerals exhibit unusual optical phenomena,…
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