ANOTHER. The Mohs’ scale is not a LINEAR scale. Instead, it ranks gems on a relative scale based on their scratch hardness.Hardness is measured by scratching the mineral with series of substances of known VARIATION in hardness USING the Mohs scale.Hardness Number for different minerals based on the Mohs scale is:MineralScale NumberTalc1Gypsum2Calcite3Fluorite4Apatite5Feldspar6Quartz7Topaz8Corundum9Diamond10 Note: A scratch with the aid of a fingernail INDICATES a hardness in the range of 2 - 3.