The examinations carried out have confirmed a relationship existing between the character of fracture surfaces and the composition and structure of (basalt and gravel) concretes. For both concretes investigated, a very good correlation was obtained between the profile line development factor, <TEX>$R_L$</TEX>, and the fracture surface development factor, <TEX>$R_S$</TEX>. With the increase in the <TEX>$R_L$</TEX> parameter, the fracture surface development factor <TEX>$R_S$</TEX> also increased. Agreement between the proposed relationship of <TEX>$R_S=f(R_L)$</TEX> and the proposal given by Coster and Chermant (1983) was obtained. Stereological examinations carried out along with fractographic examinations made it possible to obtain a statistical model for the determination of <TEX>$R_L$</TEX> (or <TEX>$R_S$</TEX>) based on the volume of air voids in concrete, <TEX>$V_{air}$</TEX>, the specific surface of air pores, <TEX>$S_V_{air}$</TEX> the specific surface of coarse aggregate, <TEX>$S_{Vagg.}$</TEX>, and the volume of mortar, <TEX>$V_m$</TEX>. An effect of coarse aggregate type on the obtained values of the profile line development factor, <TEX>$R_L$</TEX>, as well as on the relationship <TEX>$R_S=f(R_L)$</TEX> was observed. The increment in the fracture surface development factor <TEX>$R_S$</TEX> with increasing <TEX>$R_L$</TEX> parameter was larger in basalt concretes than in gravel concretes, which was a consequence of the level of complexity of fractures formed, resulting chiefly from the shape of coarse aggregate grains.