Luster is a term used in mineralogy to describe the way light interacts with the surface of a crystal, rock, or mineral). It is a physical property that can be helpful in mineral and gem identification. Luster describes how a mineral appears to reflect light and how brilliant or dull the mineral is. The terms used to describe luster are:
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Metallic: Minerals with a metallic luster are opaque and have the appearance of polished metal. Examples include gold, tin, and copper.
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Submetallic: Minerals with a submetallic luster have the look of a metal that is dulled by weathering or corrosion. Examples include galena and pyrite.
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Nonmetallic: Minerals with a nonmetallic luster do not look like metal at all. Nonmetallic luster is divided into several sub-types:
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Vitreous: Minerals with a vitreous luster have the sheen of glass. This is the most common luster in the mineral kingdom and occurs in minerals such as quartz).
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Resinous: Minerals with a resinous luster have the look of amber and are not quite glassy. Examples include sphalerite).
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Adamantine: Minerals with an adamantine luster have the hard, sparkly look of a diamond. Examples include cerussite and zircon).
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Pearly: Minerals with a pearly luster have a sheen similar to the inside of a mollusk shell or shirt button. Examples include micas.
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Silky: Minerals with a silky luster have optical properties similar to silk cloth. Examples include gypsum.
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Greasy: Minerals with a greasy luster resemble fat or grease. Examples include opal and cordierite).
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Dull: Minerals with a dull luster have poor reflective qualities, much like unglazed porcelain. Examples include kaolinite.
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Earthy: Minerals with an earthy luster exhibit little to no luster due to coarse granulations that scatter light in all directions. Examples include limonite).
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Luster is not a diagnostic property, meaning that it can vary from one specimen to another for most mineral species). However, it can be a useful hint in mineral identification and can set a person on the proper route).
