MOHS Hardness Test
Understanding the MOHS hardness test
The Mohs Hardness Scale is a widely used method for determining the relative hardness of minerals and other objects. This scale consists of ten reference minerals numbered 1 through 10, which range from a very soft mineral (talc) to a very hard mineral (diamond). The hardness of a mineral is defined as its "resistance to being scratched".
The Mohs Hardness Scale was discovered by Friedrich Mohs, a German mineralogist, in 1812. He selected the ten minerals of distinctly different hardness and found that the scale was a useful tool in determining the identity of minerals. With the exception of diamond, the minerals are all relatively common, easy to obtain, and inexpensive.
To use the Mohs Hardness Scale, begin by locating a smooth, unscratched surface for testing. Hold the specimen of unknown hardness firmly against a table top so that the surface to be tested is exposed and accessible. Then, 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.
There are four situations that might be observed when comparing the hardness of two specimens. If Specimen A can scratch Specimen B, then Specimen A is harder than Specimen B. If Specimen A does not scratch Specimen B, then Specimen B is harder than Specimen A. If the two specimens are equal in hardness, then they will be relatively ineffective at scratching one another. If Specimen A can be scratched by Specimen B but it cannot be scratched by Specimen C, then the hardness of Specimen A is between the hardness of Specimen B and Specimen C.
A list of minerals in order of hardness can be a handy reference. If you determine that a specimen has a hardness of Mohs 4, you can quickly get a list of potential minerals. Practice and experience will improve your abilities when doing this test. You will become faster and more confident.
It is essential to note that some hard materials are also very brittle. If one of your specimens is breaking or crumbling rather than scratching, you will have to be very careful while conducting the test. Testing tiny or granular specimens can also be difficult. Some specimens contain impurities. If the results of your test are not visibly conclusive, or if the information from your test does not conform with other properties, do not hesitate to do the test again. It is possible that a small piece of quartz (or another impurity) was embedded in one of your specimens.
Overall, the Mohs Hardness Scale has been used by geologists and geology students for over 200 years, and it remains a simple yet effective method for determining the relative hardness of minerals and other objects.