Ammonium nitrate finds application in explosives and chlorine-free slow-burning propellants. Different phases are known for this ammonium salt, each of them featured by peculiar bulk densities. As a consequence, the variation of storage temperature induces processes of expansion-contraction in the crystals, unless specific stabilization is performed. In this paper, a batch of raw ammonium nitrate particles has been thermally cycled between -30 degrees C to +60 degrees C and analyzed. Microscopic observations, particle size measurement, and X-ray microtomography showed that the particles undergo a progressive fragmentation process, with opening of internal cracks and voids. The tested material halved its mass-mean diameter after five thermal cycles. As a term of comparison, a phase-stabilized ammonium nitrate batch was tested under the same conditions, showing no effect.