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Heftetjernite, a new scandium mineral from the Heftetjern Pegmatite, Tordal, Norway

Uwe Kolitsch, Roy Kristiansen, Gunnar Raade and Ekkehart Tillmanns
Heftetjernite, a new scandium mineral from the Heftetjern Pegmatite, Tordal, Norway
European Journal of Mineralogy (March 2010) 22 (2): 309-316

Abstract

Heftetjernite, ideally ScTaO (sub 4) , is a new scandium mineral from the Heftetjern pegmatite, Tordal, Telemark, Norway. In the type specimen, it occurs as minute, elongate tabular, very dark brown crystals in a single small void in albite. Other associated minerals are fluorite, muscovite, altered milarite, a metamict, dark greyish brown mineral of the pyrochlore-microlite group, and an unidentified, orange-brown, tabular, nearly X-ray amorphous Ti-Y-Ta-Nb-mineral. Electron-microprobe analysis yielded the empirical formula (Sc (sub 0.64) Sn (sub 0.13) Mn (sub 0.12) Fe (sub 0.08) Ti (sub 0.06) ) (sub Sigma 1.03) (Ta (sub 0.69) Nb (sub 0.30) ) (sub Sigma 0.99) O (sub 4) which clearly demonstrates the charge-balanced substitution scheme 2Sc (super 3+) = (Sn,Ti) (super 4+) +(Mn,Fe) (super 2+) . The mineral crystallises in the wolframite structure type, with space group P2/c and a=4.784(1), b=5.693(1), c=5.120(1) Aa, beta =91.15(3) degrees , V=139.42(5) Aa (super 3) (Z=2). A synthetic equivalent is known. Strongest lines in the calculated X-ray powder diffraction pattern of heftetjernite are [d in Aa(I) (hkl)]: 3.000 (100) (11-1), 2.9570 (97) (111), 3.662 (53) (110), 2.4877 (34) (02-1), 4.783 (33) (100), 3.807 (32) (01-1). The crystal structure was refined to R(F)=1.39% from single-crystal X-ray diffraction data (293 K). It is based on two types of edge-sharing, distorted octahedra occupied predominantly by Sc and Ta, respectively. Heftetjernite is translucent to transparent, with a dark brownish (with a reddish hue) streak and adamantine lustre. It is brittle, has a perfect {010} cleavage, irregular fracture and a Mohs hardness estimated to be around 4.5 by comparison to ferberite; D (sub x) =6.44 g/cm (super 3) (from crystal-structure analysis). Optically, the mineral is biaxial with an unknown optical sign, weakly pleochroic (yellowish brown with a reddish tint to reddish brown), with no observable dispersion. A mean refractive index of 2.23 was calculated from the Gladstone-Dale relationship using the X-ray density. Heftetjernite is named after its type locality. The mineral is compared with synthetic ScTaO (sub 4) , ScNbO (sub 4) , iwashiroite-(Y) and formanite-(Y) (both nominally YTaO (sub 4) ), and some comments are made on the relation to Sc-bearing ixiolite.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 22
Serial Issue: 2
Title: Heftetjernite, a new scandium mineral from the Heftetjern Pegmatite, Tordal, Norway
Affiliation: Naturhistorisches Museum, Mineralogisch-Petrographische Abt., Vienna, Austria
Pages: 309-316
Published: 201003
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 49
Accession Number: 2010-039542
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 5 tables
N58°45'00" - N60°13'00", E07°09'00" - E09°52'00"
Secondary Affiliation: Universitetet i Oslo, NOR, NorwayUniversitaet Wien, AUT, Austria
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201022
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