Pocket Genius Rocks And Mineralspdf Hot Direct

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Central to mineral identification is the , a relative scale from 1 (softest) to 10 (hardest), created by German mineralogist Friedrich Mohs in 1812. It uses common reference points: a fingernail (2.5) , a copper penny (about 3.5) , a knife blade or window glass (5.5) , and a steel file (6.5) . pocket genius rocks and mineralspdf hot