Acta Musei Moraviae

Ranciéite and todorokite from Zvole near Bystřice nad Pernštejnem (Moravia, Czech Republic)

Investigation is focusing on a historical sample labeled “pyrolusite” from Zvole. It comes from an abandoned quarry (GPS coordinates N 49° 29.869′ E 016° 09.937′) extracting calcite marble from the Strážek Moldanubicum. Our investigation proved older information about flogopite as a main accessory mineral, followed by quartz, dolomite, chlorite, and amphibole supergroup mineral. Result of the X-ray powder diffraction analysis of manganese oxide sample is mixture of ranciéite and todorokite accompanied by calcite and quartz. Electron microscopy shows spherulitic to botryoidal aggregates of both manganese phases, frequently with concentric zoning caused by distribution of Ba and variable porosity between the extremely thin crystals. Average ranciéite formula from 8 measured spots is (Ca_0.12Ba_0.01)_Σ0.13(Mn⁴⁺_0.76□_0.24)_Σ1.00 O_2.00·0.58 H₂O, based on 2 oxygens, all manganese in tetravalent form, and water calculated from Mn / H₂O ratio from an ideal formula. Average todorokite formula from 8 measured spots is Ca_0.41Ba_0.19K_0.07Na_0.03Sr_0.01)_Σ0.70(Mn⁴⁺_0.75Mg_0.12Si_0.02Fe³⁺_0.02Al_0.01)_Σ5.74O_12.00·2.87 H₂O, based on 12 oxygens and water calculated from (Mn + Si + Mg + Fe³⁺ + Al) / H₂O ratio from an ideal formula. The origin of local manganese mineralization is linked with marble karstification, which released small (0.03 wt.% of MnO) manganese content from carbonates and fixed it in form of Mn⁴⁺ oxides.