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Smithsonite Gemology
Smithsonite with excellent color and clarity is often cut into faceted gems and cabochons. It is rarely used in jewelry because it has a Mohs hardness of only 4 to 4.5 and would be quickly scratched and abraded even with careful wear. The accompanying photos show a faceted oval of translucent yellow smithsonite and a teardrop-shaped cabochon cut…
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Smithsonite vs. Hemimorphite
Smithsonite and hemimorphite are two very different minerals. Smithsonite is a carbonate mineral and a member of the trigonal crystal system, while hemimorphite is a silicate mineral and orthorhombic. They also have noticeable differences in specific gravity and cleavage. Even with these differences, the two minerals were confused with one another and identified by the name “calamine”…
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Geologic Occurrence
Smithsonite is a secondary mineral found in the rocks above and around many important zinc deposits. These smithsonite occurrences are often seen at the surface or at shallow depths. As a result, smithsonite was one of the earliest zinc minerals to be discovered and mined by pioneer metallurgists. Finding smithsonite at the surface has led to the…
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What is Smithsonite?
Smithsonite is a zinc carbonate mineral with a chemical composition of ZnCO3. Today it is a minor ore of zinc, but in the early days of metallurgy it was one of the most important ores. Typical smithsonite colors are brown, gray, white, green, and yellow. Translucent specimens in vibrant blue, green, pink, and yellow colors are favorites…
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A Gemologist’s View of Luster
Most geologists, including the author of this article, have not thought as deeply about luster as gemologists. If you open almost any mineralogy textbook to the pages that describe a mineral, the luster is usually given as one or two of the adjectives listed above. For example: submetallic to metallic. The author completed the coursework…
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Luster Is Not Diagnostic
Luster is not a diagnostic property. This means that, for most mineral species, luster can vary from one specimen to another. For example: hematite can exhibit a metallic luster, a submetallic luster, or a dull luster. A single specimen can exhibit one or more of these lusters. Because of that, luster cannot be heavily relied…
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Commercial Use of Luster
Many minerals used in commercial products owe their value and popularity at least in part to their luster. The best example is gold. It has a highly reflective metallic luster that resists tarnish. That beautiful luster makes gold the perfect metal for jewelry manufacturing. Today, most of the world’s gold is made into jewelry. Muscovite…
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Types of Luster
The photographs and descriptions on this page illustrate some of the most common lusters observed in minerals. Metallic Luster Specimens with a metallic luster exhibit the reflectivity and brightness of a metal and are always opaque. The smoother the surface, the brighter their luster, and the higher their reflectivity. When a beam of incident light is reflected…
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How to Observe Luster
The luster of a mineral is best observed on a surface that is free of moisture, dirt, tarnish, and abrasion. Geologists in the field usually carry a rock hammer to break rocks so that their true luster and color can be observed. Breakage is usually not necessary when observing the luster of cleaned and cared-for specimens in a laboratory or classroom.…
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What Is Luster?
Luster is a word used to describe the light-reflecting characteristics of a mineral specimen. The luster of a specimen is usually communicated in a single word. This word describes the general appearance of the specimen’s surface in reflected light. Eleven adjectives are commonly used to describe mineral luster. They are: metallic, submetallic, nonmetallic, vitreous, dull, greasy, pearly, resinous,…