Scratch Hardness

The scratch hardness is commonly measured by Mohs test. The method is based upon the scale of hardness, known as Mohs scale, in which ten standard minerals are arranged in the order of their ability to be scratched. The softest mineral with scratch hardness of 1 is talc whereas the hardest mineral, diamond, has a hardness of 10 on Mohs scale. The other minerals between them in increasing order of hardness are gypsum, calcite, fluorite, appetite, feldspar, quartz, topaz, sapphier and corundum. The method of determining Mohs hardness is to compare a scratch on the material surface, produced under standardised conditions with the scratch on one of the minerals occupying position from 1 to 10 on Mohs scale. Although the test had been chiefly designed for minerals, any metal can be tested by this method. Most metals fall in mohs hardness range of 4 to 18 and it is difficult to differentiate between two metals whose hardness is close. Because of this reason this method is not well suited for metals.