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Proshchenkoite-(Y) from Russia — a new mineral species in the vicanite group: descriptive data and crystal structure

Published online by Cambridge University Press:  05 July 2018

G. Raade ,
J. D. Grice ,
M. Erambert ,
P. Kristiansson  and
T. Witzke
G. Raade*
Affiliation:
Department of Geology, Natural History Museum, University of Oslo, P.O. Box 1172, Blindern, NO-0318 Oslo, Norway
J. D. Grice
Affiliation:
Research Division, Canadian Museum of Nature, P.O. Box 3443, Station D, Ottawa Ontario K1P 6P4, Canada
M. Erambert
Affiliation:
Department of Geosciences, University of Oslo, P.O. Box 1047, Blindern, NO-0316 Oslo, Norway
P. Kristiansson
Affiliation:
Department of Nuclear Physics, Lund Institute of Technology, Box 118, SE-221 00 Lund, Sweden
T. Witzke
Affiliation:
Institut für Chemie/Technische Chemie, Universität Rostock, Albert-Einstein-Strasse 3a, DE-18059 Rostock, Germany
*
*E-mail: gunn-ra@online.no
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Abstract

A REE-bearing fluorosilicate from the Tommot REE-Nb deposit in Yakutia, Russia, described without a name in 1966, is characterized here as a new species, proshchenkoite-(Y), of the vicanite group of borosilicates. Wavelength-dispersive electron probe analyses gave the following empirical formula: Y3.70REE7.54Ca1.55Na1.16Mn0.77Th0.10Pb0.01)Σ14.83(Fe2+0.83Mn0.15Ti0.02)Σ1.00Ca1.00(P0.70Si0.26As0.04)Σ1.00Si0.26B3.20(O34.55F13.45)Σ48. Boron was analysed with a nuclear microprobe method based on the nuclear reaction 11B(p,α)2α. The simplified formula is (Y,REE,Ca,Mn)15(Fe2+,Mn)Ca(P,Si)Si6B3O34F14. The mineral is trigonal, R3m, with a = 10.7527(7) Å, c = 27.4002(18) Å, V = 2743.6(6) Å 3, Z = 3. The crystal structure was refined to Rl = 0.042 for 1819 observed reflections. Proshchenkoite-(Y) is isostructural with okanoganite-(Y), vicanite-(Ce) and hundholmenite-(Y), and the differences in site occupancies are discussed. The strongest six reflections of the X-ray powder-diffraction pattern [dobs in Å, (I), (hkl)] are: 4.441, (36), (202); 3.144, (77), (214); 3.028, (45). (009); 2.968, (100), (027); 1.782, (32), (330); and 1.713, (32), (1.2.14). The mineral is optically uniaxial (—) with ω 1.734(2) and 8 1.728(2). The Mohs hardness is about 5; density measured on material subject to incipient metamictization is 4.72 g/cm3, as compared to Dcalc = 4.955 g/cm3.

The result of electron microprobe analyses of alleged okanoganite-(Y) from the type locality in Okanogan County, Washington, USA, is also presented. We find here also that P > Si at one of the sites, whereas the analytical data of Boiocchi et al. (2004) indicate Si > P. Consequently, the mineral we have analysed is the P analogue of okanoganite-(Y), another new species.

Keywords

proshchenkoite-(Y)new mineral speciesokanoganite-(Y)vicanite groupREE borosilicateelectron-microprobe datanuclear microprobe datacrystal structureTommot REE-Nb depositRussia
Type
Research Article
Information
Mineralogical Magazine , Volume 72 , Issue 5 , October 2008 , pp. 1071 - 1082
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2008

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Footnotes

†

also at: Norwegian Mining Museum, P.O. Box 18, NO-3602 Kongsberg, Norway

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