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As hard as they come
Up to scratch? Meet Friedrich Mohs and his famed geological scale

Most readers will have heard of the Moh scale of hardness, if only through references in Review as we went through the alphabet with our A-Z of metals and minerals. Conceived in 1822, it is one of the oldest aids in mineral identification.

It is also something of a misnomer. Its inventor was an Austrian called Friedrich Mohs (not Moh), and his gift to the infant science of mineralogy was not so much a scale of hardness as an ordered list of minerals with different scratch resistances. But let's settle for the familiar and call his list by its usual name.

Moh's scale is the most lasting reminder of a dazzling scientific career. A graduate of the famous Freiberg Mining Academy, where he later succeeded his illustrious mentor Abraham Werner as professor of mining, Mohs first scaled some of the highest peaks of the academic world. Then he was commissioned by the Emperor of Austria to reorganize the imperial mineral collection, eventually becoming chancellor of the imperial exchequer for mining and mining finance.

In Mohs' time, nothing was known about the atomic structure of minerals, the underlying reason for differences in hardness. His search for a scale of hardness must have involved a great deal of trial and error. He settled on scratch resistance as the most practical measure of hardness, and looked for a set of well known minerals that spanned the whole range of natural hardness in fairly regular steps.

He knew that diamond was the hardest mineral of all. Though he was conscious that it was disproportionately harder than corundum, he could find no common mineral to bridge the gap between them. He wasn't to know it, but a mineral named after his time called moissanite (natural silicon carbide) could have neatly dropped into the gap, although it is a rarity and found mainly in metallic meteorites.



As hard as they come Up to scratch? Meet Friedrich Mohs and his famed geological scale Most readers will have heard of the Moh scale of hardness, if only through references in Review as we went through the alphabet with our A-Z of metals and minerals. Conceived in 1822, it is one of the oldest aids in mineral identification. It is also something of a misnomer. Its inventor was an Austrian called Friedrich Mohs (not Moh), and his gift to the infant science of mineralogy was not so much a scale of hardness as an ordered list of minerals with different scratch resistances. But let's settle for the familiar and call his list by its usual name. Moh's scale is the most lasting reminder of a dazzling scientific career. A graduate of the famous Freiberg Mining Academy, where he later succeeded his illustrious mentor Abraham Werner as professor of mining, Mohs first scaled some of the highest peaks of the academic world. Then he was commissioned by the Emperor of Austria to reorganize the imperial mineral collection, eventually becoming chancellor of the imperial exchequer for mining and mining finance. In Mohs' time, nothing was known about the atomic structure of minerals, the underlying reason for differences in hardness. His search for a scale of hardness must have involved a great deal of trial and error. He settled on scratch resistance as the most practical measure of hardness, and looked for a set of well known minerals that spanned the whole range of natural hardness in fairly regular steps. He knew that diamond was the hardest mineral of all. Though he was conscious that it was disproportionately harder than corundum, he could find no common mineral to bridge the gap between them. He wasn't to know it, but a mineral named after his time called moissanite (natural silicon carbide) could have neatly dropped into the gap, although it is a rarity and found mainly in metallic meteorites.
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