The Mohs scale of mineral hardness is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of minerals through the ability of harder material to scratch softer material.

The scale was introduced in 1812 by the German geologist and mineralogist Friedrich Mohs.The Mohs scale is an ordinal scale. For example, corundum (9) is twice as hard as topaz (8), but diamond (10) is four times as hard as corundum.

The hardness of a stone indicates the stone’s resistance to scratching or how the surface of the gem will respond to contact with a sharp point. This differs from a gem’s toughness, which is defined by how well a gem can survive an impact or resist breaking, chipping or cracking. We invite you to consult the GIA website to find out more about the toughness of a precise gemstone, or to contact us regarding any gemstone-related question.