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Hundholmenite-(Y) from Norway – a new mineral species in the vicanite group: descriptive data and crystal structure

Published online by Cambridge University Press:  05 July 2018

G. Raade*
Affiliation:
Department of Geology, Natural History Museum, University of Oslo, P.O. Box 1172 Blindern, NO-0318 Oslo, Norway
O. Johnsen
Affiliation:
Geological Museum, University of Copenhagen, Øster Voldgade 5-7, DK-1350 København K, Denmark
M. Erambert
Affiliation:
Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, NO-0316 Oslo, Norway
O. V. Petersen
Affiliation:
Geological Museum, University of Copenhagen, Øster Voldgade 5-7, DK-1350 København K, Denmark
*

Abstract

Hundholmenite-(Y) occurs as pale brown, subhedral crystals up to 1 mm across, embedded in REE–bearing fluorite, in a granitic pegmatite at Hundholmen, Tysfjord, Nordland County, north Norway. Two other occurrences in the same area are the granitic pegmatites at Stetind and Lagmannsvik. The simplified formula, obtained from wavelength-dispersive EMP analyses and boron determination by ICP-AES, is (Y,REE,Ca,Na)15(Al,Fe3+)CaxAs1–x3+ (Si,As5+)Si6B3(O,F)48 (x = 0.78). The mineral is trigonal, R3m, with a = 10.675(6), c = 27.02(2) Å , V = 2667(5) Å 3, Z = 3. The crystal structure was refined to R1 = 0.037 for 1720 observed reflections. Hundholmenite-(Y) is isostructural with okanoganite-(Y) and vicanite-(Ce), and the differences in site populations are discussed. The strongest seven reflections of the X-ray powder-diffraction pattern [dobs in Å , (I) (hkl)] are: 4.38 (33) (202), 3.114 (43) (214), 2.972 (100) (027), 2.947 (76) (125), 2.924 (66) (303, 033), 2.681 (36) (220) and 1.978 (37) (235). The mineral is optically uniaxial (–) with o 1.7578(5) and e 1.7487(5). The Mohs hardness is ~5–6; Dcalc = 5.206(9) g/cm3.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2007

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