Original paper

Mineral chemistry and parageneses of magnetoplumbite from the Filipstad district, Sweden

Holtstam, Dan

European Journal of Mineralogy Volume 6 Number 5 (1994), p. 711 - 724

36 references

published: Sep 28, 1994
manuscript accepted: May 2, 1994
manuscript received: Feb 9, 1994

DOI: 10.1127/ejm/6/5/0711

BibTeX file

ArtNo. ESP147050605005, Price: 29.00 €

Download preview PDF Buy as PDF


Abstract Electron-microprobe analyses of magnetoplumbite (formally PbFe12O19) from Långban-type deposits in the Filipstad district, Sweden, demonstrate that the mineral is highly variable in composition with ranges: PbO 16.1-19.8, BaO 0.1-1.5, Sb2O5 0.0-9.0, ZnO 0.0-2.1, Fe2O3 37.0-64.0, MnO 2.8-9.2, Mn2O3 0.0-22.7, Cr2O3 0.0-1.0, TiO2 0.0-10.2, Al2O3 0.0-2.6, MgO 0.1-0.8 (all in wt.%). The major mechanisms of substitution are Mn3+ = Fe3+, Mn2+ + Ti4+ = 2 Fe3+ and 2 Mn2+ + Sb5+ = 3 Fe3+. Ba is the only significant substituent for Pb with up to 0.12 atoms pfu, and the ratio between large and small (interstitial) cations is ideal within the analytical error limits. It is suggested that the coupled incorporation of high-valence and divalent cations, partitioned over different crystallographic sites, stabilizes the mineral relative to the pure ferrite. The structure appears to be incompatible with Mn3+ contents much above 3.3 atoms pfu, which is ascribed to the distorting nature of the 3d4 ion in octahedral coordination. In coexisting magnetoplumbite-jacobsite pairs Mn3+ is equally distributed, whereas in associations with melanotekite-kentrolite, Mn3+ is favoured (~ 5x) by the members of the latter series. The unit-cell volume of magnetoplumbite samples can be predicted to a few Å3 from V - 10733 + 399.3, where is the mean octahedral ionic radius of the interstitial cations. Magnetoplumbite is considered to have been formed during prograde stages of metamorphism of metasomatized, Si-depleted meta-exhalites, under conditions of high ƒo2


magnetoplumbitehexagonal ferritemineral chemistryLångban-type depositsSweden