The aim of this investigation was the selective separation of Mg(II) from olivine, (Mg,Fe)SiO4. The feasibility of leaching of Mg2+, Fe2+, and Fe3+ from olivine and serpentinized olivine with HCl or H2SO4 solutions of pH similar to 2 or 3.5 has been examined. The results obtained showed that, under identical conditions, HCl solution is more effective than H2SO4 in leaching of Mg2+ as well as Fe2+, and that the optimum pH is <3.5. Magnesium ions are selectively and quite effectively separated from the leaching solution by precipitation of Mg(OH)(2) at pH similar to 11.5 since most, if not all, other metal ions that exist in natural samples are pre-precipitated as hydroxides and separated by filteration. Alternatively, Mg2+ is selectively separated from the leaching solution by flotation as magnesium oleate in the 7.0-8.5 pH range.