This experimental work was undertaken with the aim of determining the main mechanical characteristics of the iron ores and the enclosing quartzites of the Lenin (formerly Kolachevskii) mine in the Krivoy Rog district. The experiments carried out made it possible to establish: 1) The independence of the forms of failure of rock cubes solely from the nature of the packings. 2) The delay of compressive deformation under high loads. 3) An almost complete proportionality between elastic deformation and stress in most samples at unit loads exceeding 50–150 kg/cm², and some deviation from this strict proportionality at lower loads, which in general agrees with the aforementioned conclusions of E. E. Woo. 4) The constancy of Poisson's ratio with increasing load, and its determination for iron ore and quartzite by means of a special modification of the Martens mirror apparatus. 5) The excess of residual transverse deformations over elastic ones, and the excess of elastic deformations over residual ones in the direction of compression.