In 1812 Friedrich Mohs, a mineralogist, developed a scale to help identify various minerals by testing their hardness against 10 specific minerals of significantly different hardness. Based how easily a mineral in question is scratched or scratches helps to determine its classification, because most minerals of a similar type will share the same hardness. Rated 1-10 (see below), 1 being the softest, these minerals are used because, although diamonds are quite expensive, all 10 are fairly common and fairly easy to obtain.


The test is conducted as follows:

A sharp point of Mineral A is used to attempt to scratch Mineral B. If Mineral A can scratch Mineral B, then Mineral A is harder than Mineral B. If Mineral A does not scratch Mineral B, then Mineral B is harder than Mineral A. If the two Minerals are equally ineffective at scratching one another, then they are the same hardness. If Mineral A can be scratched by Mineral B but it cannot be scratched by Mineral C, then the hardness of Mineral A is between the hardness of Mineral B and Mineral C.


A similar test can be conducted using more common objects that have been classified by their comparison to the 10 minerals (see below).


Why is this important to us in the stone world? Because when specifying a product for counter tops, flooring, exterior cladding, etc., a person needs to understand the characteristics of said product, and how it will respond to the specific needs of their project. This information among other things, can help a customer make an educated decision on the type of product they want in their home or business, and avoid costly and/or aesthetically unpleasant issues down the road.


For example:

Soapstone is a beautiful product that is chemically innate making it ideal for kitchens, as a lot of foods contain acids. However, because of the varying amounts of talc in it, its hardness typically rates between a 2 to 4, making it fairly easy to scratch. So in spite of how much a person may love the look and feel of soapstone, if they can’t embrace its susceptibility to scratching, it may not be the best product for them.


By comparison, granite is an igneous rock comprised mostly of quartz and feldspar, and a small mix of mica and other minerals. This product is quite difficult to scratch, rating 7. However, because the classification of “granite” has been commercially simplified to a stone that is harder than marble but still similar to true granite, this introduces a wider mix of minerals, and so, rates between 5.5 to 7. It is a far more practical choice for many projects in regards to hardness, and by including stones like gneiss, schist, pegmatite, and basalts, among others, it is also an extremely beautiful choice.


The Mohs hardness scale and common scale are as follows: