What is luster in mineralogy ?

Luster : definition

Luster is the visual perception of how a mineral reflects light. By analogy with shards of characteristic substances, we speak of metallic luster (in the case of many sulphides), vitreous (most silicates), adamantine (reminiscent of diamond), resinous, pearly, silky, earthy, waxy, etc... The brightness may differ depending on the planes affected by the reflection phenomenon : crystalline face, cleavage plane, aggregate of crystals of more or less large sizes.

Luster is a property almost independent of the color of the mineral, which directly depends on the refractive index and absorption coefficient for opaque minerals.

The degrees of intensity of the luster of the minerals correspond faithfully to the following values of the average refractive indices:

- vitreous luster : index from 1.3 to 1.9
- adamantine luster : index from 1.9 to 2.6
- sub-metallic luster: index from 2.6 to 3
- metallic luster : index greater than 3

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