In this work microwave irradiation on cylindrical samples of basaltic rock is investigated by laboratory experiments and compared with results from numerical models. Due to the temperature gradient in the samples induced by the microwave irradiation a significant damage indicated by a reduction of the sound velocity and finally the formation of cracks occurs. Applying a microwave power of 3.2 kW leads to a surface temperature of 250 degrees C and to 400 degrees C in the centre of a cylindrical sample after 60 s of irradiation. Temperature rise goes along with the formation of both axial and radial cracks. Cracks are not bound to the mineralogical composition but their development is governed by macroscopic temperature gradients and the geometry of the sample. A thermal and a thermomechanical finite element model are formulated and used to calculate temperature distributions and induced thermal stresses. The results indicate that tensile stresses exceed tensile strength leading to cracks as observed experimentally. (C) 2012 Elsevier Ltd. All rights reserved.