How Hard is Your Stone? What You Need to Know About the Mohs Hardness Scale

Why is it that marble scratches easier than quartzite? Is quartzite harder than granite? To first begin to answer these questions, quarries and stone suppliers begin with the Mohs Hardness Scale to help classify a natural stone.

What is the Mohs Hardness Scale?
The Mohs Hardness Scale was developed in 1812 by a German geologist and mineralogist, Friedrich Mohs to determine the relative hardness of a mineral as a comparison to another mineral. For example, the scale begins with the softest material, talc. All materials above talc have the ability to scratch talc. The second material is gypsum, and since talc is below gypsum, talc is softer and thus not able to scratch gypsum. As you move up the scale the minerals become harder and harder, ending with the strongest mineral: diamond.

What else should I consider when determining my stone’s strength?
Understanding the strength of a slab is not black and white. While the Mohs Hardness Scale is certainly a worthwhile resource to provide a general guideline, it does not provide all of the information for a natural stone slab. The Mohs Hardness Scale only takes into consideration the strength of a single mass element – or the purest form of each mineral. This is like asking, “what is the flavor of Neapolitan ice cream?” And while, in general, your quartzite is harder than your granite, or your granite is harder than your marble, keep in mind that natural stone is a product of mother nature. Meaning, no two slabs are alike and each has its own similar, yet unique composition. This composition, much like human DNA, is what makes each stone a beautiful, unique work of art.

How does a quarry classify stone?
When a stone is purchased from the quarry, the quarry will provide a report with the geologic makeup of the stone. If the majority of the minerals in the large block of stone is quartzite, than the quarry will classify the slab as a quartzite.

Use the Mohs Hardness Scale when you are evaluating which stone is right for you to get a general idea of where to begin. As with all natural stones, there is never a guarantee of hardness or “scratch proof” material. In order to prevent scratches and maintain the lifetime of your natural stone, we always recommend researching and finding the best sealer that will meet your needs.

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