hardness test वाक्य

Hardness tests are inadvisable for three reasons : glass is fairly soft ( typically 6 or below ) and can be scratched by a large number of materials ( including many simulants ); diamond has four directions of perfect and easy cleavage ( planes of structural weakness along which the diamond could split ) which could be triggered by the testing process; and many diamond-like gemstones ( including older simulants ) are valuable in their own right.