The paper reports on experimental study of peridotites with different average grain sizes. It is shown that coarse-crystalline peridotite undergoes multiple bulk fracture along all large fragments, whereas fracture of fine-crystalline peridotite is localized in the centre and develops in a direction close to the compression axis with the only slight deflection to directions of maximum tangential stresses in the upper and lower parts in which the zone of localized deformation is bifurcated. It is found that by the onset of fracture, the lateral to axial strain ratio for the coarse- and fine-crystalline specimens is 1.36 and 0.76, respectively.
