Eleonorite, Fe-6(3+) (PO4)(4)O(OH)(4)center dot 6H(2)O: validation as a mineral species and new data

摘要

Eleonorite ideally Fe-6(3+)(PO4)(4)O(OH)(4)6H(2)O the analogue of beraunite Fe2+Fe53+(PO4)(4)(OH)(5)6H(2)O with Fe2+ completely substituted by Fe3+ has been approved by the International Mineralogical Association Commission on New Minerals Nomenclature and Classification as a mineral species (IMA 2015-003). The mineral was first described on material from the Eleonore Iron mine Dunsberg near Giessen Hesse Germany but during this study further samples were required and a neotype locality is the Rotlaufchen mine Waldgirmes Wetzlar Hesse Germany where eleonorite is associated with goethite rockbridgeite dufrenite kidwellite variscite matulaite planerite cacoxenite strengite and wavellite. Usually eleonorite occurs as red-brown prismatic crystals up to 0.2 mm x 0.5 mm x 3.5 mm in size and in random or radial aggregates up to 5 mm across encrusting cavities in massive 'limonite'. The mineral is brittle. Its Mohs hardness is 3. D-meas = 2.92(1) D-calc = 2.931 g cm(-3). The IR spectrum is given. Eleonorite is optically biaxial (+) alpha= 1.765(4) beta= 1.780(5) gamma = 1.812(6) 2Vmeas = 75(10)degrees 2V(calc) = 70 degrees. The chemical composition (electron microprobe data H2O analysed by chromatography of products of ignition at 1200 degrees C wt.%) is: Al2O3 1.03 Mn2O3 0.82 Fe2O3 51.34 P2O5 31.06 H2O 16.4 total 99.58. All iron was determined as being trivalent from a Mssbauer analysis. The empirical formula (based on 27 O apfu) is (Fe-5.76(3+) Al0.18Mn0. 093+)(Sigma 6.03)(PO4) O-3.92(OH)(4.34)5.98H(2)O. The crystal structure (R = 0.0633) is similar to that of beraunite and is based on a heteropolyhedral framework formed by M(1-4) phi(6)-octahedra (where M= Fe3+; O= O2- OH- or H2O) and isolated PO4 tetrahedra with a wide channel occupied by H 2 O molecules. Eleonorite is monoclinic space group C2/c a = 20.679(10) b = 5.148(2) c = 19.223(9) angstrom beta = 93.574(9)degrees V = 2042.5(16) angstrom(3) and Z = 4. The strongest reflections of the powder X-ray diffraction pattern [d angstrom (I%) (hkl)] are 10.41 (100) (200) 9.67 (38) (002) 7.30 (29) (202) 4.816 (31) (111 004) 3.432 (18) (600 114 404 313) 3.197 (18) (510 511 006 314 602) 3.071 (34) (314 115).