Microhardness analysis of halite from different salt-bearing formations

Microhardness tests were carried out on single halite crystals. They were conducted on the (001) surface, with the indenter set in two directions: parallel to the halite face (010); and parallel to the (110) face. The halite crystals represent salt formations of different ages (Devonian, Zechstein, Badenian), depths (from 1835.5 to 195 m) and intensities of tectonic disturbance (horizontally stratified, salt dome, strongly folded). The measurement results revealed specific features of the halite crystals analysed. Firstly, the data obtained show microhardness anisotropy in halite crystals. Moreover, microhardness correlates with the depth of the salt-bearing formations. Halite crystals from deeper levels showed higher microhardness, though there was no correlation between the intensity of tectonic deformation and the average Vickers hardness (HV). The samples analysed show a variability of HV values and and of the shapes of imprints. These indicate zones where halite crystals are deformed at the atomic level and reflects the presence of defects in the crystal lattice. Such deformation is reflected in an irregularity of the strike of cleavage planes. Consequently, the analysis of imprint shapes is a useful method for the examination of ductile minerals and materials.