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Friedrich Moh's laboratory notes, handwritten. Amongst other things, he invented the Moh's scale for hardness, diamond being 10 and Talc being 1. This was in 1822, in Graz. Iron is between 4 and 5 on this scale, although this clearly depends on microstructure. For example, a hardened steel file has a Moh's hardness in excess of 7.