1, the solid material composed of chemical bonds, by a combination of shared electrons Covalent bonds, combined with the strongest, therefore the maximum hardness of Covalent crystals such as diamond and silicon carbide;
2, formed by combining specific ion-gravity of ionic crystals, its hardness with the construct ion electricity price increases, ion the shortened for space, as well as enhanced polarization increases, but the material's hardness is hardness of Covalent crystals to small;
3, by free electrons between metal atoms combine to form metallic bonds, because the bond is relatively weak, so the hardness of metals in the middle-low position;
4, by the molecular attraction between particles combine to form molecular bonds, because the bond is the weakest, so minimum hardness of molecular crystals, such as graphite, talc, kaolinite. Depending on the hardness measurement, can be expressed as the scratch hardness, hardness, abrasive hardness, its numerical measurements varies, but its variation similarity, characterized by hardness and greater value.