This test is different from the field hardness test and the attrition test. This test is carried out in Dorry’s testing machine. A cylinder of 25 mm of the stone is rubbed against a steel disc spindled with coarse sand. The specimen is subjected to a pressure of 1.25 kg/mm2. After 1000 revolutions in the machine, the loss in weight is found, and the coefficient of hardness is determined as
Coefficient of hardness = 
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