FE-RICH LANGBANITE FROM THE NYBERGET ORE-FIELD, SWEDEN

Iron-rich langbanite from the Nyberget ore-field carrying romeite incl usions coexists with hematite, albite, braunite, garnet, and clinopyro xene on fissures cutting banded braunite - hematite - garnet ore. Mono clinic cell parameters are: a = 11.535(5) angstrom, b = 20.003(7) angs trom, c = 11.150(6) angstrom, beta = 89.89(7)-degrees, V = 2572.7(3.4) angstrom3. An average composition may be given as: (Mn2+3.86,Ca2+0.10 ,Mg2+0.01)(Mn3+5.78,Fe3+3.10, Ti4+0.03)Sb5+1.08Si4+1.96O2-24showing th e highest iron content known for this phase. The investigated crystal is chemically homogeneous. The chemical composition of romeite inclusi ons in langbanite is: (Ca2+1.19,Na+0.54,Mn2+0.16)(Sb5+2.01,Fe3+0.09, T i4+0.01)O6(O0.62, OH0.38). Intergrown with romeite an unknown phase oc curs with major Ca, Sb and Pb and minor Mn, Fe, Bi, Si, Ti and Na. Mos sbauer spectroscopy shows that no ferrous iron is present in the langb anite structure. MS-spectra recorded at room and low (77K) temperature indicate that high spin ferric iron occupies three different octahedr ally coordinated Mn(2) sites of the monoclinic structure (as proposed by Giuseppetti et al. 1991). No iron is found in the Mn(3) sites.