The Mohs Hardness Test and Scale were invented in 1812 by the German mineralogist Fredrich Moh[Ref1,2] as a means to rank minerals according to their relative hardness in resisting scratching. Its ease of use has resulted in its wide application by mineral collectors and lapidarists. The ten-point scale begins with the softest mineral talc assigned a hardness of 1 and ends with the hardest mineral diamond assigned a hardness of 10. Minerals with intervening hardness values between 2 and 9 are: gypsum (selenite) at a hardness of 2, calcite at 3, fluorite at 4, apatite at 5, orthoclase (feldspar) at 6, quartz at 7, topaz at 8, and corundum (ruby, sapphire) at 9. In Figure 1 shows the hardness scale, and as well, includes everyday objects of known hardness which can also be used in hardness testing[Ref2]. The relative hardness values are obtained by determining which mineral scratches one of lesser hardness and is scratched by a mineral or an object of greater hardness. Testing is done by placing a sharp point of one mineral or another testing agent against the surface of another and attempting to scratch it. One of the following results may be observed:
If mineral A scratches mineral B then A is harder than B.
If A doesn’t scratch B then B is harder than A.
If A and B are relatively ineffective in scratching each other they are of equal hardness.
If A can be scratched by B but not by C the hardness o A is between the hardness of B and C.
The Mohs Hardness Test is performed using the steps and tips as described in
Figures 2 and as shown live in the YouTube video accompanying this brief presentation. An example of testing using a knife and a penny are described in Figure3.
REFERENCES
Ref 1. https://en.wikipedia.org/wiki/Friedrich_Mohs
Ref2. https://geology.com/minerals/mohs-hardness-scale.shtml
Ref 3. https://www.lindahall.org/friedrich-mohs/
Ref 4. https://www.nbc12.com/story/17003531/jens-coin-story/
]]>