Minerals and Gems Ranked by Hardness

A mineral’s hardness—its resistance to scratching—is measured by its Mohs number. One hundred major minerals and gems are ranked from soft to hard in this Mohs scale spiral. Since nothing on earth is harder than diamond, the spiral ends in the middle.

German mineralogist Friedrich Mohs developed the scale in 1812 to help identify unknown minerals. The scale is relative—essentially based on differentiating which stone can scratch another. If a mineral can scratch another mineral, it is positioned higher on the scale.

The scale in non-linear and the numbers are more like ranks rather than a scale where the gap between each progressive number is equal. Diamond, the hardest mineral, is over 4 times harder than sapphire, for example. But the difference between talc, the softest mineral, and sapphire is less, even though they are 9 numbers apart.

The circled minerals are the baseline reference mineral for each number, as chosen by Mohs. He simply selected ten inexpensive and common minerals that varied in hardness and arbitrarily placed them on an integer scale from 1 to 10. 

Students use Mohs mineral kits containing all 10 baseline stones to test specimens.

NOTE:

–Many of the minerals have a range on the scale. For example malachite ranges from 3.5 to 4. For this chart, I used the smaller of the two numbers if there was a range.

–Ruby and sapphire are types of corundum.