Mohs Hardness Scale E book

 

Mohs Hardness Scale E book, A list of popular crystals with their hardness

The Mohs Hardness Scale is used as a convenient way to help identify minerals. A mineral’s hardness is a measure of its relative resistance to scratching, measured by scratching the mineral against another substance of known hardness on the Mohs Hardness Scale. This graphic outlines the index minerals and some common objects that are used to determine a mineral’s hardness.

This method is especially useful for identifying minerals in the field because you can test minerals against some very common objects (fingernail, a penny, a nail). The scale is named for its creator, the German geologist and mineralogist Friedrich Mohs. However, the method of comparing hardness has been used as far back as 300 BC

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 hardness of 5.

By doing successive tests with different reference specimens, you can closely estimate the Mohs hardness of your mineral specimen. The Mohs hardness of a mineral is important information for determining the identity of your specimen.

Mohs Hardness Scale E book

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 Mohs Hardness Scale minerals. The Mohs Hardness Scale has been used by geologists and geology students for over 200 years. Millions of students have used the Mohs Hardness Test to identify minerals. It is surprising that such a simple test has been in use for over two centuries.

Mohs Hardness Testing Procedure

• • Begin by locating a smooth, unscratched surface for testing.

 

• • With one hand, hold the specimen of unknown hardness firmly against a table top so that the surface to be tested is exposed and accessible. The table top supports the specimen and helps you hold it motionless for the test. (If you are doing this test at a nice desk you may want to get a thick piece of cardboard, a thick rubber pad, or a sheet of some other material to protect the surface from being scratched.)

 

• • Hold one of the standard hardness specimens in the other hand and place a point of that specimen against the selected flat surface of the unknown specimen.

 

• • Firmly press the point of the standard specimen against the unknown specimen, and with firm pressure, drag the point of the standard specimen across the surface of the unknown specimen.

 

• • Examine the surface of the unknown specimen. With a finger, brush away any mineral fragments or powder that was produced. Did the test produce a scratch? Be careful not to confuse mineral powder or residue with a scratch. A scratch will be a distinct groove cut in the mineral surface, not a mark on the surface that wipes away. Use a hand lens to get a good look at what happened.

 

• Conduct the test a second time to confirm your results.

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