The impulses of mechanoluminescence caused by stressing of fine quartz particles in the stirred mill were analysed. An obtained distribution of light impulse can be described by means of the powder function with two different exponents, one for low and other one for high impulse amplitude. The critical amplitude in between remains constant at all investigated process parameters. The observed difference in exponents reflects a different behaviour under applied stress for fine and coarse particles. An intensive production of pores and microcracks occurs during the wet treatment of fine particles. The light emission from stressed particle decreases with growth of pores inside of particles. Consequently, the number of counted stress events at a given impulse amplitude, is reduced. Also, the frequency of impulse decreases with growth of pores. A ratio of current to start impulse frequency reflects the grad of development of pore structure. An intensive particle size reduction occurs when this ratio achieves a critical magnitude. Particle size distribution becomes three-modal instead of bimodal at start of grinding. The third mode with maximum at 100 nm appears due to fracture of porous particles. (C) 2004 Kluwer Academic Publishers.