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GEOREF RECORD

Beltrandoite, a new root-name in the hogbomite supergroup; the Mg end-member magnesiobeltrandoite-2N3S

Fernando Camara, Roberto Cossio, Daniele Regis, Valerio Cerantola, Marco E. Ciriotti and Roberto Compagnoni
Beltrandoite, a new root-name in the hogbomite supergroup; the Mg end-member magnesiobeltrandoite-2N3S
European Journal of Mineralogy (September 2017) 30 (3): 545-558

Abstract

Magnesiobeltrandoite-2N3S, ideally Mg6Al (sub 20) Fe (sub 2) (super 3+) O (sub 38) (OH) (sub 2) , is a new member of the hogbomite supergroup of minerals. It occurs in magnesian chloritites of a metamorphosed layered mafic complex in the Etirol-Levaz continental slice, middle Valtournenche, Aosta Valley, Italy. Magnesiobeltrandoite-2N3S grows in a fine-grained chlorite matrix associated as inclusions to relict pre-Alpine hercynite spinels and dolomite in cm- to dm-long darker boudins, which are cut by corundum + clinochlore + or - dolomite veins. It occurs as subhedral to euhedral black crystals ( approximately 50-400 mu m), dark reddish-brown in thin section. It shows dark brown streak and vitreous lustre. It is brittle, with no cleavage observed and uneven fracture. Mohs hardness approximately 6-61/2. D (sub calc) = 3.93 g . cm (super -3) It shows no fluorescence under UV radiation and no cathodoluminescence. The mineral is optically uniaxial (-) with an estimated mean refractive index of ca. 1.80. Pleochroism is weak with epsilon = deep reddish brown (along c axis) and omega = reddish brown (perpendicular to c). Absorp> is E > O. The Raman spectrum shows a weak and strongly polarized broad OH-characteristic absorption centered at 3364 cm (super -1) . Electron microprobe analysis combined with Synchrotron Mossbauer source spectrometry yielded the following empirical formula based on 40 anions per formula unit (pfu) [Al (sub 18.36) Mg (sub 3.96) Fe (super 2+) (sub 2:52) Fe (super 3+) (sub 2:08) Ti (sub 0.56) Cr (sub 0.40) Zn (sub 0.06) V (super 3+) (sub 0:03) Mn (sub 0.02) ] (sub Sigma 28) O (sub 38) (OH) (sub 2) . The ideal formula is Mg (sub 6) Al (sub 20) Fe (sub 2) (super 3+) O (sub 38) (OH) (sub 2) . The eight strongest lines in the X-ray powder diffraction pattern are [d (sub obs) / A(l) (I) (hkl)]: 2.858 (42) (110), 2.735 (51) (107), 2.484 (46) (018), 2.427 (100) (115), 1.568 (29) (128), 1.514 (30) (0212), 1.438 (42) (2013), and 1.429 (72) (220). The crystal structure of magnesiobeltrandoite-2N3S [P3 (super -) m1, a = 5.7226(3), c = 23.0231(9)A, V = 652.95(5)A (super 3) ] was refined from X-ray single-crystal data to R1 =0.022; it is isostructural with magnesiohogbomite-2N3S.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 30
Serial Issue: 3
Title: Beltrandoite, a new root-name in the hogbomite supergroup; the Mg end-member magnesiobeltrandoite-2N3S
Affiliation: Universita degli Studi di Milano, Dipartimento di Scienze della Terra "A. Desio", Turin, Italy
Pages: 545-558
Published: 20170925
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 30
Accession Number: 2017-087759
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 9 tables, geol. sketch map
N45°49'36" - N45°49'36", E07°34'51" - E07°34'51"
Secondary Affiliation: Canada, Geological Survey, CAN, CanadaEuropean Synchrotron Radiation Facility, FRA, FranceAssociazione Micromineralogica Italiana, ITA, Italy
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2022, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201746
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