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Magnesiobermanite, MgMn3+2(PO4)2(OH)2⋅4H2O, the Mg analogue of bermanite: Description and crystal structure

Published online by Cambridge University Press:  13 December 2021

Peter Elliott Open the ORCID record for Peter Elliott [Opens in a new window]
Peter Elliott*
Affiliation:
Department of Earth Sciences, School of Physical Sciences, The University of Adelaide, Adelaide, South Australia 5005, Australia South Australian Museum, North Terrace, Adelaide, South Australia 5000, Australia
*
*Author for correspondence: Peter Elliott, Email: [email protected]
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Abstract

Magnesiobermanite, MgMn3+2(PO4)2(OH)2⋅4H2O, is a new secondary phosphate mineral and the Mg analogue of bermanite found in a granitic pegmatite at the White Rock No.2 quarry situated in the Bimbowrie Conservation Park, South Australia, Australia. Magnesiobermanite occurs as aggregates of twinned, bladed to tabular crystals, up to 1.2 mm across. Individual crystals are up to 0.3 mm in length. The crystals are orange–red to brownish red, with a vitreous lustre and a salmon-pink streak. The mineral is brittle with a conchoidal fracture and a good cleavage on {100}. The mineral is biaxial (–), with α = 1.690(2), β = 1.719(2) and γ = 1.734(2) (white light). The calculated 2V is 70.4°. Electron microprobe analyses provided: MgO 9.59, Mn2O3 27.41, Fe2O3 8.84, Al2O3 0.18, P2O5 33.27, H2O 20.94, total 100.23 wt.%. The empirical formula (based on 14 O atoms) is: Mg1.02(Mn3+1.49Fe3+0.47Al0.02)1.98(PO4)2.01(OH)1.95⋅4.01H2O. Magnesiobermanite is monoclinic, space group P21, with the unit-cell parameters: a = 5.4215(11), b = 19.072(4), c = 5.3889(11) Å, β = 110.21(3)°, V = 522.89(18) Å3 and Z = 2. The crystal structure was refined to an R1 index of 2.43% based on for 3222 observed reflections with Fo > 4σ(Fo). Magnesiobermanite is isostructural with bermanite, Mn2+Mn3+2(PO4)2(OH)2⋅4H2O, from which it derives its name. The structure is based upon a sheet of the form [(M(OH)2(PO4)2] in the (010) plane. Sheets are linked in the b direction by [M3(H2O)4O2] octahedra and by hydrogen bonds.

Keywords

magnesiobermanitenew mineral speciesmagnesium manganese phosphatepegmatitecrystal structureWhite Rock No.2 quarryAustralia
Type
Article
Information
Mineralogical Magazine , Volume 86 , Issue 1 , February 2022 , pp. 127 - 133
Copyright
Copyright © The Author(s), 2021. Published by Cambridge University Press on behalf of The Mineralogical Society of Great Britain and Ireland

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Footnotes

Associate Editor: David Hibbs

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