Hardness refers to the resistance of a smooth surface of a rock or mineral to scratching. It is determined by the binding force of atoms within the crystal structure abd is measured according to Moh’s ten division scale of hardness, ranging from 1 the softest, to 10 the hardest: 1) talc 2) gypsum 3) calcite 4) fuorite 5) apatite 6) orthoclase 7) quartz 
topaz 9) corundum 10) diamond.
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