The present work reports the results of so called “impact experiments” on nine different kinds of crystals, five inorganic salts and four organic acids, performed by letting ten crystals fall through an evacuated tube onto a glass plate. The ratio between the abraded volume of a crystal and the volume of the crystal itself is inversely proportional to the plasticity index of the material. The size distribution of the fragments, in terms of number density function vs. size, is well fitted for all the systems by a power law equation with an order equal to - 2.82