This paper presents the results of laboratory controlled weathering of fine and coarse grained diabase samples. Under pH and temperature control diabase fragments were leached by drops of aqueous solution The experiment was carried out with rocks of similar mineralogical composition but different grain sizes. The main mineral composition was: plagioclase (An55-60), pyroxene (augite and pigeonite), locally altered to homblend, opaques (magnetite and elmenite), besides small amounts of apatite, clay minerals and interstitial micropegmatite. The grain size of the fine grained diabase (DI) was 0,1 - 1,0 mm and the corse grained (D2) about 1,0 -10,0 mm. The following decreasing relative mobiliti of elements was observed by comparisons between the chemical composition of the original diabases and the leached ones: D1 - Fine grained Ca >; K >; Mg >; Na >; Si >; Fe>; Al D2 - Coarse grained Ca >; Na >; K >; Si>; Mg >; Fe>; Al
