Laboratory experiments on rock samples have shown electric signal emissions when the samples are subjected to temporal stress increase especially when the samples approach failure. These electric signals are attributed to the generation and propagation of microcracks that guide the sample to mechanical failure. In this work the temporal evolution of electric charge release is studied for marble samples subjected to stress at a constant rate up to fracture and it is correlated to the respective recordings of the yielded strain. The results exhibit a systematic linear correlation between electric charge and deformation, with a constant proportionality factor independent of stress rate magnitude. This linear correlation, which is in accordance with the Moving Charged Dislocations (MCD) model, exists from the instant that the marble samples are driven to the non-linear region of mechanical behaviour due to the applied stress, and more precisely to the Crack Propagation Zone (CPZ) up to the prefailure phase.