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Mohs Hardness Testing Procedure
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Making Hardness Comparisons
“Hardness” is the resistance of a material to being scratched. The test is conducted by placing a sharp point of one specimen on an unmarked surface of another specimen and attempting to produce a scratch. Here are the four situations that you might observe when comparing the hardness of two specimens: 1. If Specimen…
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Discovering a Hardness Scale
Friedrich Mohs, a German mineralogist, discovered the hardness scale in 1812. He selected ten minerals of distinctly different hardness that ranged from a very soft mineral (talc) to a very hard mineral (diamond). With the exception of diamond, the minerals are all relatively common, easy to obtain, and inexpensive. See the accompanying table of the…
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How the Mohs Scale Works
If you have a mineral specimen of unknown hardness, and reference mineral #5 can scratch it, then the hardness of your specimen is less than or equal to a Mohs hardness of 5. Similarly, if your specimen cannot be scratched by reference mineral #5, then its hardness is greater than or equal to a Mohs…
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What is Mohs Hardness Scale?
The Mohs Hardness Scale is a set of ten reference minerals (numbered 1 through 10) that are used to determine the relative hardness of minerals and other objects. In this test the hardness of a mineral is defined as its “resistance to being scratched”. A list of the Mohs Hardness Scale Minerals is shown in the table…
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Hemimorphite vs. Smithsonite
Although hemimorphite and smithsonite are different minerals with different chemical compositions and crystal structures, they have frequently been confused – especially when only simple tools were available and the specimens could not be subjected to destructive testing. Often a single specimen will be an intergrown mixture of hemimorphite and smithsonite. Until the mid-to-late 1800s, the…
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Gemology
Hemimorphite is a favorite collector gem because it occurs in a range of spectacular colors. Some collectors seek out specimens that will cover the full range of hemimorphite’s colors. Hemimorphite should be used cautiously in jewelry. It has a Mohs hardness of only 4 ½ to 5, so it will be quickly abraded if worn in a ring or…
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Crystal Habit
Hemimorphite exhibits a variety of crystal habits, including prismatic, tabular, and botryoidal. The crystals are often blade shaped and grow in clusters. These clusters can form a fan-like spray of blade-shaped crystals; a cockscomb similar to marcasite; or, tightly intergrown, radiating clusters that produce a botryoidal habit.
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Physical Properties of Hemimorphite
If you attend a mineral show or visit a museum, you will see hemimorphite specimens with beautiful crystals and in spectacular colors. Most hemimorphite has an unremarkable appearance. It usually occurs in a massive or granular habit and is white, gray, colorless or brown in color. Individual crystals, when distinguishable, can be prismatic, tabular and…
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Geologic Occurrence of Hemimorphite
Most hemimorphite is found in the rocks above and surrounding zinc deposits. Here, primary zinc ores such as sphalerite were altered to produce hemimorphite as a weathering product, or secondary mineral. Some hemimorphite is also formed where zinc-bearing rocks were subjected to metasomatism. Hemimorphite can occur as crusts that replaced primary sulfide minerals, crusts of crystals that…