Manganese Sturmanite from the N’Chwaning 2 Mine, Kalahari, South Africa

Gritsenko, Y.D.; Dedushenko, S.K.; Vigasina, M.F.; Pautov, L.A.; Golubev, Y.V.; Ogorodova, L.P.; Ksenofontov, D.A.; Melchakova, L.V.; Perfilyev, Y.D.

Авторы: Gritsenko Yu D., Dedushenko S.K., Vigasina M.F., Pautov L.A., Golubev Ya V., Ogorodova L.P., Ksenofontov D.A., Melchakova L.V., Perfilyev Yu D.
Журнал: Geology of Ore Deposits
Том: 65
Номер: 7
Год издания: 2023
Издательство: Maik Nauka/Interperiodica Publishing
Местоположение издательства: Russian Federation
Первая страница: 1
Последняя страница: 12
DOI: 10.1134/S1075701523070036
Аннотация: The oxidation state of Mn is determined for the first time by iodine titrimetry, and the Mn4+/Mn3+ ratio (54/46%) is identified for Mn-sturmanite from the N’Chwaning 2 Mine (Kalahari manganese field,South Africa). The Mössbauer spectrum of sturmanite, which contains a single asymmetric Lorentz doublet with parameters RTISα-Fe = 0.31(1) mm/s, RTQS = 0.18(1) mm/s, FWHML = 0.55 mm/s, and FWHMR = 0.33 mm/s, confirms the presence of Fe3+ only in the composition of the mineral. The process of its thermal transformation is studied using thermal analysis and IR spectroscopy: dehydration and decomposition of Ca polyhedra, dehydroxilation, decarbonatization, and complete decomposition of structure with the formation of anhydrite, hematite, and Ca borates occur up to 200, 600, 750, and 1000°C, respectively. The chemical formula of the studied sturmanite, which is recalculated on the basis of our studies to eight cations, is as follows:Ca5.94 Al0.03Si0.02[B(OH)4]1.00[B(OH)3] 0.11[SO4]2.32[СО3]0.49(OH)12 ⋅ 22.7H2O. The unit cell parameters of the mineral are determined using X-ray powder diffraction: a = 11.148(3), c = 21.830(9) Å, and V = 2349(2) Å3. The unit cell parameters of minerals of the sturmanite–jouravskite series linearly decrease with an increasing mole amount of the jouravskite endmember. It is suggested that the studied mineral can be an intermediate member of the sturmanite–jouravskite series with heterovalent isomorphic substitution according to following schemes: Mn3+ and Mn4+ → Fe3+ in the cation octahedral site and [CO3]2– → [B(OH)4]– and [SO4]2– in the anion site.
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Manganese Sturmanite from the N’Chwaning 2 Mine, Kalahari, South Africaстатья

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