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Geology

The Mohs Hardness Scale: Comparing the hardness of minerals

Infographic on the Mohs Mineral Hardness Scale. The graphic shows the scale, which runs from 0-10, and also highlights a number of minerals with their point on the scale. Key reference minerals for each point on the scale are also shown: 1 = talc, 2 = gypsum, 3 = calcite, 4 = fluorite, 5 = apatite, 6 = feldspar, 7 = quartz, 8 = topaz, 9 = corundum, 10 = diamond.
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Diamond is commonly known to be the hardest material, but how do other minerals compare with each other? That’s the question the Mohs hardness scale, introduced by Friedrich Mohs in 1812, aims to answer. This graphic looks at his scale and where different minerals and other substances appear on it.

Mohs’ scale is a simple way of comparing the hardness of different minerals. The scale is built on comparisons — a mineral that scratches another is designated as having a higher value for hardness. These values are essentially a giant ranking system, in that they’re all relative. There’s no fixed value of hardness between the different numbers in the scale — in fact, diamond at 10 is several times harder than corundum at 9, but corundum is only around twice as hard as topaz at 8.

You’d be forgiven for wondering, given this variability between points on the scale, what its use is. It’s particularly useful for geologists in the field who can use known reference materials or minerals to scratch unknown minerals and estimate where on the scale they sit, aiding their identification.

Some of the additional items I’ve included on the scale in the graphic are relevant to the reference materials geologists may use — for example, fingernails, copper coins, steel knives, and ceramic streak plates. I’ve also included some other non-mineral substances on the scale for reference, such as some common metals and some other materials noted for their high hardness, like tungsten carbide.

Is diamond really the hardest material known? In terms of naturally-occurring substances, the answer appears to be yes, though lab-grown materials are providing potential challengers, as this article summarises.

I’ll finish by concluding that I’m not a geologist, and this isn’t intended to be a comprehensive chart — there are many more minerals out there than it was possible to include on it! However, I’ve tried to include a representative spread of minerals. Shout in the comments if you’ve noted any glaring omissions!

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