| Title | Beltrandoite, a new root-name in the hogbomite supergroup: the Mg end-member magnesiobeltrandoite-2N3S |
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| Author | Camara, F ;
Cossio, R; Regis, D; Cerantola, V; Ciriotti, M E; Compagnoni, R |
| Source | European Journal of Mineralogy vol. 30, 3, 2018 p. 545-558, https://doi.org/10.1127/ejm/2017/0029-2692  Open Access |
| Image |  |
| Year | 2018 |
| Alt Series | Natural Resources Canada, Contribution Series 20200189 |
| Publisher | E Schweizerbartsche Verlagsbuchhandlung |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Area | Valtournenche; Aosta Valley; Italy |
| Lat/Long WENS | 7.5000 7.6000 45.8333 45.7500 |
| Subjects | mineralogy; Nature and Environment; Science and Technology; minerals; morphology, crystal; crystallinity; electron probe analyses; electron microscope analyses |
| Illustrations | location maps; tables; spectrograms; spectra; sections; digital images; distribution diagrams; structure stereograms |
| Released | 2017 09 22 |
| Abstract | Magnesiobeltrandoite-2N3S, ideally Mg6Al20Fe23+O38(OH)(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 dolomite veins. It occurs as subhedral to euhedral black crystals (similar to 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 approximate to 6-61/2. D-calc = 3.93 g.cm(-3) . It shows no fluorescence under LTV 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). Absorption is E > O. The Raman spectrum shows a weak and strongly polarized broad OH-characteristic absorption
centred at 3364 cm(-1) . Electron microprobe analysis combined with Synchrotron Mossbauer source spectrometry yielded the following empirical formula based on 40 anions per formula unit (pfu)
[Al18.36Mg3.96Fe2.522+Fe2.083+Ti0.56Cr0.40Zn0.06V0.033+Mn0.02](Sigma 28)O-38(OH)(2). The ideal formula is Mg6Al20Fe23+O38(OH)(2).The eight strongest lines in the X-ray powder diffraction pattern are [d(obs)/angstrom (l) (h k l)]: 2.858 (42) (110),
2.735 (51) (107), 2.484 (46) (018), 2.427 (100) (1 15), 1.568 (29) (128), 1.514 (30) (0212), 1.438 (42) (2013), and 1.429 (72) (220). The crystal structure of magnesiobeltrandoite-2N3S [P (3) over bar ml, a = 5.7226(3), c = 23.0231(9) angstrom, V =
652.95(5) angstrom(3)] was refined from X-ray single-crystal data to RI = 0.022; it is isostructural with magnesiohogbomite-2N3S. |
| GEOSCAN ID | 326601 |
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