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Mineral Identification: Luster

Mineral luster is a property used to characterize and identify minerals based on their appearance when light interacts with their surfaces. Luster refers to the way light is reflected from a mineral’s surface, and it can be described using various terms, each reflecting a specific appearance. Here are the most common types of mineral luster. (slide show with examples below)

1. Metallic Luster: Minerals with metallic luster appear as if they are made of metal and reflect light in a manner similar to polished metals. The reflection is bright, shiny, and typically opaque, giving the mineral a metallic appearance. Common minerals with metallic luster include galena (lead sulfide), pyrite (fool’s gold), and native copper.

2. Non-Metallic Luster: Non-metallic luster encompasses a wide range of appearances that do not resemble metals. It can be further subdivided into various types.

a. Vitreous Luster: Vitreous luster gives minerals a glassy appearance, resembling the luster of a broken piece of glass. The reflections are bright and transparent to translucent. Quartz and feldspar are examples of minerals with a vitreous luster.

b. Pearly Luster: Minerals with pearly luster exhibit a soft, iridescent glow reminiscent of a pearl’s shine. This luster is usually seen on the surface of cleavage planes and is common in minerals like talc and muscovite mica.

c. Silky Luster: Silky luster imparts a fibrous or fibrous-satin appearance, creating a sheen similar to silk fabric. Minerals like satin spar gypsum and fibrous forms of chrysotile asbestos display silky luster.

d. Greasy Luster: Greasy luster gives minerals a wet and oily appearance. The reflections are muted and subdued, and the mineral surface seems to lack transparency. Minerals like nepheline and serpentine can exhibit greasy luster.

e. Resinous Luster: Resinous luster provides minerals with a glow similar to resin or certain types of plastic. The reflections are bright but not as sharp as vitreous luster. Amber and sphalerite are minerals with resinous luster.

f. Waxy Luster: Waxy luster imparts a soft, smooth, and dull shine, resembling the appearance of wax. Minerals like hydrozincite and cerussite can exhibit waxy luster.

g. Adamantine Luster: Adamantine luster creates a brilliant, almost sparkling reflection, giving the mineral a diamond-like appearance. Diamond itself is the best-known example of a mineral with adamantine luster.

Luster is an important diagnostic property for mineral identification, as it can help differentiate minerals with similar colors and other physical properties. By observing the luster of a mineral along with other characteristics such as hardness, color, and cleavage, mineralogists can confidently identify and classify minerals, contributing to our understanding of Earth’s diverse geological processes and mineralogical diversity.

Slideshow on luster