How do we measure the Hardness of Materials ?
Meaurement of Hardness of Material
Hardness is a characteristic property of the solid objects. It is measured by the resistance which the body offers to anything which tends to scratch it. The hardness of the various materials is measured either on the mohs scale or the knoop scale. Mohs scale is numbered from 1 to 10 that is it gives ten grades of hardness. In this scale diamond is the harest material and talc is the softest. Diamond has a hardness of 10 mohs and talc has a hardness of 1 mohs. The mineralogists carry a box containing pieces of the above minerals for testing samples in the field.
For example: If they find a mineral that can be scratched by feldspar but not by apetite, its hardness lies between 5 and 6 on the hardness scale. To measure hardness in the knoop scale an elongated diamond-shaped indenting device is employed to measure the indentation it makes in a given test material. By this method the hardness of extremely brittle materials including glass and even diamond can be measured without damaging either the indenter or the test piece. The size of the indentation is taken as a measure of the materials hardness.