Manganrockbridgeite, Mn2+2Fe3+3(PO4)3(OH)4(H2O), a new member of the rockbridgeite group, from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria
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Published:2023-04-25
Issue:2
Volume:35
Page:295-304
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ISSN:1617-4011
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Container-title:European Journal of Mineralogy
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language:en
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Short-container-title:Eur. J. Mineral.
Author:
Grey Ian E., Hochleitner Rupert, Kampf Anthony R.ORCID, Boer Stephanie, MacRae Colin M.ORCID, Cashion John D.ORCID, Rewitzer Christian, Mumme William G.
Abstract
Abstract. Manganrockbridgeite,
Mn22+Fe33+(PO4)3(OH)4(H2O), is a new
member of the rockbridgeite group, from the Hagendorf-Süd 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 µm long and 20 µm 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
α= 1.795(5), β= 1.805(calc), γ=1.815(5)
(white light) and 2V(meas.) = 90(2)∘. The empirical formula from
electron microprobe analyses, Mössbauer spectroscopy and crystal
structure refinement is
(Mn1.072+Fe0.692+Fe0.163+)Σ1.92(Fe3+)2.88(PO4)3(OH)3.64(H2O)1.44.
Manganrockbridgeite has monoclinic symmetry with space group P21/m and
unit-cell parameters a=5.198(2), b=16.944(5), c=7.451(3) Å,
β=110.170(9)∘, V=616.0(4) Å3 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+ / 50 % vacancies in M3-site octahedra forming face-shared
chains along the 5.2 Å axis, monoclinic manganrockbridgeite has full
ordering of Fe3+ and vacancies in alternate M3 sites along the 5.2 Å
axis.
Publisher
Copernicus GmbH
Subject
Pulmonary and Respiratory Medicine,Pediatrics, Perinatology and Child Health
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