luster

Luster is a property of a material that describes the way its surface reflects light. In mineralogy, luster is a diagnostic characteristic used to identify minerals and to distinguish them from other substances. It results from the interaction of light with the atomic structure and the nature of the bonds within the material, and it can vary widely across different specimens.

The most common categories of mineral luster are metallic and non‑metallic. Metallic luster, typical of minerals such as pyrite, galena, and native gold, gives a reflective, mirror‑like appearance resembling polished metal. Non‑metallic luster is subdivided into several types. Adamantine luster, seen in diamond and cerussite, is exceptionally brilliant and highly reflective. Vitreous luster resembles glass and is characteristic of quartz and calcite. Pearly luster, found on mica sheets and talc, presents a soft, iridescent sheen reminiscent of a pearl. Resinous luster appears on minerals like sphalerite and resembles the surface of hardened resin. Silky luster, observed in fibrous minerals such as asbestos, produces a sheen similar to silk. Subadamantine and greasy lusters describe intermediate or oily appearances.

Luster can be altered by surface conditions; polishing typically enhances metallic and vitreous qualities, while weathering or oxidation may dull the surface and obscure the original luster. In gemology, luster contributes to a gemstone’s visual appeal and market value, together with other optical properties such as brilliance and fire. The systematic description of luster aids geologists, mineralogists, and collectors in the classification and appreciation of solid materials.