Wakefieldite-(Ce) replacing vanadium-bearing omphacite in the ultra-oxidized manganese deposit of Prabornaz

database, nuove specie, discrediti,
ridefinizioni, classificazioni, ecc.
Rispondi
Avatar utente
Marco E. Ciriotti
Messaggi: 26988
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
Contatta:

Wakefieldite-(Ce) replacing vanadium-bearing omphacite in the ultra-oxidized manganese deposit of Prabornaz

Messaggio da Marco E. Ciriotti » gio 20 feb, 2020 20:41

Prossima pubblicazione.

Referenza:
▪ Tumiati, S., Merlini, M., Godard, G., Hanfland, M., Fumagalli, P. (2'020): Orthovanadate wakefieldite-(Ce) in symplectites replacing vanadium-bearing omphacite in the ultra-oxidized manganese deposit of Praborna (Aosta Valley, Western Italian Alps). American Mineralogist, 105, (in press).
Marco E. Ciriotti

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

Avatar utente
Marco E. Ciriotti
Messaggi: 26988
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
Contatta:

Re: Wakefieldite-(Ce) replacing vanadium-bearing omphacite in the ultra-oxidized manganese deposit of Prabornaz

Messaggio da Marco E. Ciriotti » sab 01 ago, 2020 18:20

Pubblicazione effettuata.

Referenza:
▪ Tumiati, S., Merlini, M., Godard, G., Hanfland, M., Fumagalli, P. (2'020): Orthovanadate wakefieldite-(Ce) in symplectites replacing vanadium-bearing omphacite in the ultra-oxidized manganese deposit of Praborna (Aosta Valley, Western Italian Alps). American Mineralogist, 105,

Abstract:
Because of their unique structure and properties, rare-earth (REE) orthovanadates have been extensively employed for decades in advanced ceramics, in particular in the laser industry in replacement of Nd:YAG. A Ca-bearing REE orthovanadate with the empirical formula (Ce0.279Ca0.271Y0.267Gd0.057 Nd0.055 Dy0.032Sm0.027La0.020Th0.027Sr0.002)(V5+0.908Cr3+0.067Fe3+0.017As5+0.005)O4⸱nH2O has been found in metacherts from Praborna (Italian Alps) as micrometer-sized euhedral crystals in clinopyroxene + plagioclase symplectites replacing eclogite-facies vanadium-bearing omphacite (Aegirine55–48Jadeite42–33Diopside10–8 with V2O3 ≤ 1.39 wt%). We applied the synchrotron radiation, single crystal, micro-diffraction technique, recently optimized at ID09A beamline (ESRF, France), to determine the crystal structure of this mineral. It is tetragonal and isostructural with zircon, with a = 7.2233(12) Å, c = 6.3949(18) Å, V = 333.66(13) Å3, Z = 4, space group I41/amd, and it has been therefore identified as Ca- and Y-bearing wakefieldite-(Ce) (ideally CeV5+O4). Cell parameters are in agreement with those of synthetic Ce0.7Ca0.3VO4. Raman spectra of the studied wakefieldite-(Ce) are comparable with natural and synthetic wakefieldite-(Ce) spectra and revealed the presence of OH groups and/or water of hydration, which is also suggested by the low totals in microprobe analyses. Mass balance indicates that wakefieldite-(Ce) is a by-product of the omphacite breakdown; omphacite and Mn-rich epidote, a minor reactant, provided vanadium and REE, respectively. Petrological observations and thermodynamic modeling suggest that the mineral, coexisting with hematite, Mn-rich epidote, and braunite, formed during retrogression to greenschist-facies conditions at ultra-oxidized conditions (DFMQ ≥ +16 log units), which are often observed in Mn-oxide ores. Wakefieldite is an effective scavenger of REE in oxidized geological environments at P-T conditions that range from sedimentary to medium-grade metamorphic settings, even where the REE bulk concentration is negligible. Its rarity reflects both the overall low abundance of vanadium and the need for ultra-oxidized conditions that are rarely achieved in metamorphic rocks, where REE phosphates (i.e., monazite, xenotime) are commonly found instead.

NdR: Wakefieldite-(Ce) è stata identificata tra i campioni raccolti da Matteo Giai alla miniera abbandonata di Fe-Mn di Montaldo di Mondovì (Tesi 2019 (discussa ad aprile 2020) - Dipartimento di Scienze della Terra - Università degli Studi di Torino: relatori Marco E. Ciriotti / Emanuele Costa).
Marco E. Ciriotti

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

Rispondi

Chi c’è in linea

Visitano il forum: Nessuno e 3 ospiti