Manganrockbridgeite, Mn22+Fe33+(PO4)3(OH)4(H2O), a newmember of the rockbridgeite group, from the Hagendorf-Sud pegmatite,Oberpfalz, Bavaria

Manganrockbridgeite, Mn22+Fe33+(PO4)(3)(OH)(4)(H2O), is a new member of the rockbridgeite group, from the Hagendorf-Sud pegmatite, Oberpfalz, Bavaria. It occurs in association with frondelite, kenngottite, hureaulite and hematite. It forms compact intergrowths and clusters of shiny greenish black blades up to 200 mu m long and 20 mu m wide but only a few micrometres thick. The crystals are elongated on [100] and flattened on {001}, with perfect cleavage parallel to {001}. Individual thin blades are green in transmitted light and red under crossed polars. The calculated density is 3.40 g cm(-3). Manganrockbridgeite is biaxial (+/-), with alpha = 1.795(5), beta = 1.805(calc), gamma = 1 :815(5) (white light) and 2 V (meas.) = 90(2)degrees. The empirical formula from electron microprobe analyses, Mossbauer spectroscopy and crystal structure refinement is (Mn1.072+Fe0.692+Fe0.163+)(Sigma 1.92)(Fe3+)(2.88)(PO4)(3)(OH)(3.64)(H2O)(1.44). Manganrockbridgeite has monoclinic symmetry with space group P2(1)/m and unit-cell parameters a = 5.198(2), b = 16.944(5), c = 7.451(3) angstrom, beta = 110.170(9)degrees, V = 616.0(4) angstrom(3) and Z = 2. The crystal structure was refined using both laboratory and synchrotron single-crystal diffraction data. Whereas other rockbridgeite-group minerals have orthorhombic symmetry with a statistical distribution of 50% Fe3+ C / 50% vacancies in M3-site octahedra forming face-shared chains along the 5.2 angstrom axis, monoclinic manganrockbridgeite has full ordering of Fe3+ and vacancies in alternate M3 sites along the 5.2 angstrom axis.

Automated summary

Manganrockbridgeite, a new member of the rockbridgeite group, is found in the Hagendorf-Sud pegmatite in Bavaria. It forms compact shiny greenish black blades and has monoclinic symmetry. The crystal structure of manganrockbridgeite differs from other rockbridgeite-group minerals in terms of Fe3+ and vacancies ordering.