IMA 2016-073 = magnesiobeltrandoite-2N3S

database, nuove specie, discrediti,
ridefinizioni, classificazioni, ecc.
Avatar utente
Marco E. Ciriotti
Messaggi: 24481
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy

IMA 2016-073 = magnesiobeltrandoite-2N3S

Messaggio da Marco E. Ciriotti » sab 23 set, 2017 14:59

Prossima pubblicazione.

▪ Cámara, F., Cossio, R., Regis, D., Cerantola, V., Ciriotti, M.E., Compagnoni, R. (2018): Beltrandoite, a new root-name in the högbomite supergroup: the Mg end-member magnesiobeltrandoite-2N3S. European Journal of Mineralogy, 30, (in press).

Magnesiobeltrandoite-2N3S, ideally Mg6Al20Fe23+O38(OH)2, is a new member of the högbomite 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 (∼50–400μm), 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 ≈6–6½. Dcalc = 3.93 g · cm-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 ε = deep reddish brown (along c axis) and ω = reddish brown (⊥ 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 Mössbauer source spectrometry yielded the following empirical formula based on 40 anions per formula unit (pfu) [Al18.36Mg3.96Fe2+2:52Fe3+2:08Ti0.56Cr0.40Zn0.06V3+0:03Mn0.02]Σ28O38(OH)2. The ideal formula is Mg6Al20Fe23+O38(OH)2. The eight strongest lines in the X-ray powder diffraction pattern are [dobs/A (I) (h k l)]: 2.858 (42) (1 1 0), 2.735 (51) (1 0 7), 2.484 (46) (0 1 8), 2.427 (100) (1 1 5), 1.568 (29) (1 2 8), 1.514 (30) (0 2 12), 1.438 (42) (2 0 13), and 1.429 (72) (2 2 0). The crystal structure of magnesiobeltrandoite-2N3S [P3-m1, a = 5.7226(3), c = 23.0231(9)Å, V = 652.95(5)Å3] was refined from X-ray single-crystal data to R1 = 0.022; it is isostructural with magnesiohögbomite-2N3S.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

Avatar utente
Messaggi: 6109
Iscritto il: ven 13 gen, 2006 11:39
Località: via A.Cantele n.15 35129 PADOVA

Re: IMA 2016-073 = magnesiobeltrandoite-2N3S

Messaggio da TOSATO FABIO » dom 24 set, 2017 14:24

Complimentissimi a tutti.
Tosato Fabio
"Il vero viaggio di scoperta non consiste nel cercare nuove terre, ma nell'avere nuovi occhi." M. Proust
Noi siamo anche quello che non siamo riusciti ad essere.
Sic transit gloria mundi.


Chi c’è in linea

Visitano il forum: Bing [Bot] e 4 ospiti