AbstractThe microhardness of PbTe, PbSe, EuS and EuSe has been determined. The microhardness vs lattice constant plot for chalcogenides is a curve similar to the one for alkali halides. The Gilman‐Chin parameter (H/C44) has been calculated for a large number of crytals with NaCl structure. There is no unique value representing the entire group of crystals, the values ranging from 0.01 to 0.20.The Gilman‐Chin parameter broadly correlates with the effective ionic charge (e) indicating that it is a measure of the ionicity. Empirically, it is observed that the product (H/C44) · (e)2is approximately cons