Minerals are ranked according to their Mohs hardness. Mohs hardness is a measure of a mineral's ability to resist scratching or abrasion. The Mohs hardness scale is most commonly used to rank the hardness of gemstones and minerals.
In 1812, a German mineralogist named Fredrich Moh came up with the Mohs scale to grade minerals by their hardness. The gemstones or minerals are graded on a scale of 1 to 10 when using the Mohs hardness method. Hardness is not the same as durability; a diamond is the hardest known natural mineral and can scratch almost anything, but a diamond is brittle and can be easily shattered with a hammer. The hardness can depend on the purity of the mineral. The Mohs scale uses commonly known minerals to represent each number. Number 1 is talc, 2 is gypsum, 3 is calcite, 4 is fluorite, 5 is apatite, 6 is feldspar, 7 is quartz, 8 is topaz, 9 is corundum and 10 is diamond. A mineral with a certain hardness rating scratches other minerals with the same or lower hardness ratings. A hardness test can be done by scratching the mineral against other minerals and comparing the results to the Mohs hardness scale. There are also other things to use that are cheaper and more readily available. For example, a fingernail has a hardness rank of 2.5, a copper penny is 3, a glass plate or steel knife is 5.5 and a steel file has a hardness rank of 6.5. When performing a hardness test, the mineral should be scratched against the softest object first and on to the next until it is scratched by the diamond.