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Crystal Chemistry of Schoonerite-Group Minerals

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Crystal Chemistry of Schoonerite-Group Minerals Eur. J. Mineral. 2018, 30, 621–634 Minerals and materials: Published online 27 April 2018 building principles and applications Crystal chemistry of schoonerite-group minerals 1,* 2 3 1 IAN EDWARD GREY ,ANTHONY R. KAMPF ,ERICH KECK ,COLIN M. MACRAE , 4 5 JOHN D. CASHION and YESIM GOZUKARA 1 CSIRO Mineral Resources, Private Bag10, Clayton, Victoria, 3169, Australia *Corresponding author, e-mail: [email protected] 2 Mineral Sciences department, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, California 900007, USA 3 Algunderweg 3, 92694 Etzenricht, Germany 4 Monash University, School of Physics and Astronomy, Victoria 3800, Australia 5 CSIRO Manufacturing, Private Bag 10, Clayton South, Victoria 3169, Australia Abstract: Synchrotron single-crystal structure refinements for five schoonerite-group minerals (SGMs) from the Hagendorf Süd, Bavaria, and Palermo No.1, New Hampshire, pegmatites were combined with results from previous studies on type schoonerite and the SGMs wilhelmgümbelite and schmidite to evaluate the main crystallochemical relations between the minerals. Elements Zn and Fe3þ are essential to the structure and are ordered in specific sites, while Mn and Fe are distributed relatively uniformly over three octahedral sites, M1, M2andM3. The Mn/(Mn þ Fe) atomic ratio is relatively constant for the samples studied, ∼0.26–0.31, and is close to this ratio in the primary phosphate, triphylite, from which the SGMs are derived. The main crystallochemical variations are due to different degrees of oxidation of the Fe, which ranges from 45% of the total Fe as Fe3þ in green SGMs, to 98% of the Fe as Fe3þ in red SGMs. The Fe oxidation state is linked to a significant structural change, whereby Zn in a trigonal bipyramidal site, [5]Zn, is partially partitioned into an adjacent tetrahedral site, [4]Zn, when the amount of Fe as Fe3þ increases above 70% There is an apparent correlation between the extent [4] [5] of partitioning of Zn, and cation deficiency in the M3 site, leading to a general formula for SGMs: [ (Zn,Fe)x (Zn,Fe)1Àx] M1 M2 3þ (M31Àx□x)Fe (PO4)3(OH)y(H2O)9Ày · 2H2O; where □ = vacancy and x 0.3. The sites M1, M2andM3 contain varying amounts of Fe2þ,Fe3þ,Mn2þ and Zn, with minor Mg. The different SGMs are distinguished by the dominant-cations and their oxidation states in the 3þ 3þ 2þ ¼ð 3þ 2þÞ; M1, M2andM3 sites. Wilhelmgümbelite has M1=Fe , M2=Fe , M3=Fe , while schmidite has M1 Fe0:5Mn0:5 ¼ð 3þ 2þÞ; 2þ 2þ 2þ M2 Fe0:5Mn0:5 M3 = Zn and schoonerite has M1=Mn , M2=Fe , M3=Fe . One of the SGMs studied was found to have a ¼ð 3þ 2þÞ; ¼ð 3þ 2þÞ; 2þ new ordering of dominant-cations of dominant-valency, with M1 Fe0:5Mn0:5 M2 Fe0:5Mn0:5 M3=Mn , and it has subsequently been approved as the new mineral wildenauerite (IMA 2017-058). Key-words: schoonerite; schmidite; wilhelmgümbelite; wildenauerite; Hagendorf Süd pegmatite; Palermo No.1 pegmatite; crystal structure; Mössbauer spectroscopy. 1. Introduction is orthorhombic, with a = 11.12, b = 25.55 and c =6.44A; the structure was solved in space group 2þ 3þð Þ ð Þ ð Þ ⋅ ; Pmab, an alternative setting of Pbcm. It has a complex Schoonerite, ZnMnFe2 Fe PO4 3 OH 2 H2O 7 2H2O was first described as a new species from the Palermo No. layer structure, illustrated in Fig. 1, in which 6.4 A 1 pegmatite, New Hampshire, by Moore & Kampf (1977). chains of edge-sharing M2- and M3-centred octahedra fi 2þ The type specimen was found in a corroded triphylite pod (normal to the gure) containing Fe are linked along in which the triphylite had been replaced by siderite and [100] by corner-sharing to 6.4 A chains comprising 2þ the hydrated Fe -containing phosphate minerals ludla- alternating corner-linked P2O4 tetrahedra and M4- 3þ mite, messelite and vivianite. Brown to copper-red centred octahedra (M4=Fe ). Five-coordinated [5] schoonerite laths and other oxidized secondary phosphates Zn polyhedra, Zn, share an edge with the P2O4 2þ were perched on the earlier-formed Fe -containing tetrahedra. A second phosphate group, P1O4,cross- [5] minerals. The essential Zn in schoonerite was considered links the M2- and M4-centred octahedra with Zn, and 2þ to derive from sphalerite, which is a common constituent with isolated M1-centred octahedra containing Mn , of the phosphate pods. forming {010} slabs as shown in Fig. 1.Watermole- Kampf (1977) determined the structure of schoon- cules are located between the {010} heteropolyhedral erite and noted its structural relationship to montgo- slabs and hydrogen bond to oxygen atoms at the surface meryite, olmsteadite and melonjosephite. Schoonerite of the slabs. 0935-1221/18/0030-2707 $ 6.30 https://dx.doi.org/10.1127/ejm/2018/0030-2707 © 2018 E. Schweizerbart’sche Verlagsbuchhandlung, D-70176 Stuttgart.
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