Brendelite, (Bi,Pb)₂Fe^3+,2+O₂(OH)(PO₄), a new mineral from Schneeberg, Germany: description and crystal structure

Autor(en)

Werner Krause, Heinz-Jürgen Bernhardt, Catherine McCammon, Herta Silvia Effenberger

Abstrakt

Brendelite was found on specimens from the dumps of the Gueldener Falk mine near Schneeberg, Saxony, Germany. The new mineral shows monoclinic holohedral symmetry and forms idiomorphic crystals (£0.3 mm) and crystal aggregates (£3 mm) which are frequently grown on crusts of eulytite; assocd. minerals are bismutite and bismutoferrite. The crystals of brendelite are tabular on {.hivin.201}, with addnl. forms of {001}, {010}, and {100}. The color is black to dark brown, the streak is light brown, and the luster is vitreous to adamantine. The Mohs' hardness is 4.5. No cleavage was obsd. Brendelite is biaxial neg., 2V = 70(5)° (from extinction curves), nx = 2.06, ny = 2.15 (calc.), nz = 2.19 (from reflectivity measurements). Z is II to [010] and Y is »II to [100]. Pleochroism is strong with Y = Z = dark brown to opaque and X = light brown to brown. The d. could not be measured due to lack of material; d. (calc.) = 6.83 g/cm3. Electron-microprobe analyses gave an av. of (in wt.-%) Bi2O3 47.10, PbO 26.08, FeO (calc.) 3.12, Fe2O3 9.44, P2O5 10.71, As2O5 0.32, V2O5 0.24, and H2O (calc.) 1.46, sum 98.47. A Moessbauer measurement yielded a molar ratio Fe3+:Fe2+ = 3.5:1. The empirical formula based on 7 O atoms is (Bi1.27Pb0.74).sum.=2.01(Fe3+0.74Fe2+0.27).sum.=1.01[02.00(OH)1.00].sum.=3.00.[(PO4)0.95(AsO4)0.02(VO4)0.02].sum.=0.99 and the simplified formula as derived from chem. analyses and crystal structure investigation is (Bi,Pb)2Fe3+,2+O2(OH)(PO4). Brendelite is monoclinic with space group C2/m, a = 12.278(2), b = 3.815(1), c = 6.899(1) .ANG., beta = 111.14(1)°, V = 301.4(1) .ANG.3, and Z = 2. The structure investigation was performed on single-crystal x-ray data. An av. structure was obtained showing a site disorder of the phosphate group and the hydroxyl group. An ordered structure model can be derived based on a doubled cell parameter b. FeO6 octahedra and PO4 tetrahedra are corner connected to Fe2(Oo)4(Oh)2(PO4)2 chains parallel [010]. They are linked by H bonds in (100). Edge connected (Bi,Pb)[1+4]O5 polyhedra form (Bi,Pb)2(Oo)2(Op)2 chains parallel to [010]. Both types of chains share corners and edges with each other.

Organisation(en)

Institut für Mineralogie und Kristallographie

Externe Organisation(en)

Ruhr-Universität Bochum (RUB), Universität Bayreuth

Journal

Mineralogy and Petrology

Band

63

Seiten

263-277

Anzahl der Seiten

15

ISSN

0930-0708

Publikationsdatum

1998

Peer-reviewed

Ja

ÖFOS 2012

105113 Kristallographie, 105116 Mineralogie

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/8cba896d-510d-4e40-9100-2162984c1969