AND KJELL GATEDALXenos Mineral, Ra Ê gvägen 7, SE-713 34 Nora, Sweden
ABSTR ACTThe La Ê ngban, Nordmark and Jakobsberg Mn-Fe deposits contain the only known occurrences of filipstadite and manganostibite (ideal formulae (Mn, Mg) 2 (Sb 5+ 0.5 Fe 3+ 0.5 )O 4 and Mn 2+ 7 SbAsO 12 , respectively). Filipstadite from Nordmark is newly recognized, and occurs in assemblages with svabite-johnbaumite, calcite, tephroite-forsterite, phlogopite-kinoshit alite, tilasite, +jacobsite, +plumb-ian roméite, +adelite, +hedyphane. Manganostibite from La Ê ngban and Jakobsberg is reported for the first time, and the mineral is generally associated with katoptrite, tephroite, humite-group minerals, calcite, svabite, allactite, manganosite, hausmannite, jacobsite, spinel s.s., etc. Whereas filipstadite is clearly secondary relative to the major part of the matrix components, manganostibite is believed to have formed coevally with the principal ore and skarn minerals at these deposits.The previously known compositional ranges are extended. Based on electron-microprobe analyses, Nordmark filipstadite contains 4.1 7.3 MgO, 0.0 0.5 Al 2 O 3 , 30.5 45.3 MnO, 17.0 40.1 Fe 2 O 3 , 0.2 0.9 ZnO, 19.9 29.9 Sb 2 O 5 (all in wt.%), corresponding to 58 100 mol.% of a pure filipstadite component. Associated jacobsites show Sb 2 O 5 contents of up to c. 5 wt.%. Manganostibites (all three deposits considered) contain 1.0 2.9 MgO, 2.8 3.8 SiO 2 , 57.4 60.3 MnO, 0.2 3.5 Mn 2 O 3 , 0.3 2.0 Fe 2 O 3 , 0.0 2.4 ZnO, 21.5 23.0 Sb 2 O 5 , 7.7 10.0 As 2 O 5 (all in wt.%).Si and trivalent cations are incorporated via a (Mn 3+ ,Fe 3+ ) + Si 4+ = Mn 2+ + As 5+ exchange mechanism, which improves the local charge-balance at tetrahedral structural sites dominated by As.