Scanning electron microscopy, energy dispersion spectroscopy, X-ray diffractometry and magnetometry methods were used to investigate the structure and magnetic properties of iron ore and schungite rock. The results show the existence of external size effect in iron ore concentrate. It is related with the penetration of iron nanoparticles from equipment surfaces onto the powder surface, which increases specific magnetic saturation of the powder by 1.6 times compared with pure magnetite. As a result of internal size effect in schungite powder its reactivity decreases by 800 С and after heat treatment of the powder its specific magnetic saturation increases by seven times. Considering the application of size effects the investigated powders and waste natural mineral powders are recommended to be used in the production of composite materials.