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Recognition and approval of potassic-richerite, an amphibole supergroup mineral, from the Pajsberg mines, Filipstad, Sweden.
Swedish Museum of Natural History, Department of Geology.ORCID iD: 0000-0003-2109-2277
Università degli Studi di Milano.
Swedish Museum of Natural History, Department of Geology.
Swedish Museum of Natural History, Department of Geology.
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2019 (English)In: Mineralogy and Petrology, ISSN 0930-0708, E-ISSN 1438-1168, Vol. 113, p. 7-16Article in journal (Refereed) Published
Abstract [en]

Potassic-richterite, ideally AKB(NaCa)CMg5TSi8O22W(OH)2, is recognized as a valid member of the amphibole supergroup (IMA CNMNC 2017–102). Type material is from the Pajsberg Mn-Fe ore field, Filipstad, Värmland, Sweden, where the mineral occurs in a Mn-rich skarn, closely associated with mainly phlogopite, jacobsite and tephroite. The megascopic colour is straw yellow to grayish brown and the luster vitreous. The nearly anhedral crystals, up to 4 mm in length, are pale yellow (non-pleochroic) in thin section andoptically biaxial (−), with α = 1.615(5), β = 1.625(5), γ = 1.635(5). The calculated density is 3.07 g·cm−1. VHN100 is in the range 610–946. Cleavage is perfect along {110}. EPMA analysis in combination with Mössbauer and infrared spectroscopy yields the empirical formula (K0.61Na0.30Pb0.020.93(Na1.14Ca0.79Mn0.07)Σ2(Mg4.31Mn0.47Fe3+0.20)Σ5(Si7.95Al0.04Fe3+0.01)Σ8O22(OH1.82F0.18)Σ2 for a fragmentused for collection of single-crystal X-ray diffraction data. The infra-red spectra show absorption bands at 3672 cm−1 and 3736 cm−1 for the α direction. The crystal structure was refined in space group C2/m to R1=3.6% [I >2σ(I)], with resulting cellparameters a = 9.9977(3) Å, b = 18.0409(4) Å, c = 5.2794(2) Å, γ = 104.465(4)°, V = 922.05(5) Å3 and Z=2. The A and M(4) sites split into A(m) (K+), A(2/m) (Na+), A(2) (Pb2+), and M(4′) (Mn2+) subsites, respectively. The remaining Mn2+ is strongly ordered at theoctahedrally coordinated M(2) site, possibly together with most of Fe3+. The skarn bearing potassic-richterite formed at peak metamorphism, under conditions of low SiO2 and Al2O3 activities and relatively high oxygen fugacities.

Place, publisher, year, edition, pages
Springer, 2019. Vol. 113, p. 7-16
Keywords [en]
Potassic-richterite, Amphibole supergroup, Crystal structure, Skarn, Pajsberg, Långban-type deposit
Keywords [sv]
kali-richterit, amfibol, kristallstruktur, skarn, Pajsberg, Långban-typ
National Category
Geology
Research subject
The changing Earth
Identifiers
URN: urn:nbn:se:nrm:diva-3600DOI: 10.1007/s00710-018-0623-6OAI: oai:DiVA.org:nrm-3600DiVA, id: diva2:1375847
Available from: 2019-12-06 Created: 2019-12-06 Last updated: 2019-12-06Bibliographically approved

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Holtstam, DanSkogby, HenrikKarlsson, AndreasLanghof, Jörgen
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