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The Mohs hardness scale was introduced in 1822 and is still used as a classification for
some minerals. It simply consists of 10 minerals arranged in order from 1 to 10. Diamond is
rated the highest and is indexed as 10. Talc is the softest with an index number of 1. Each
mineral in the scale will scratch those with a lower number. A completely arbitrary scale, the
Mohs hardness has little value to an engineer. Copper would be in the 2 to 3 range, iron would
be between 3 to 4 and hardened steels are in the 7 to 8 range. Some Mohs testers were built many
years ago but they are no longer known to exist.
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