IMA 2020-056 = princivalleite

database, nuove specie, discrediti,
ridefinizioni, classificazioni, ecc.
Rispondi
Avatar utente
Marco E. Ciriotti
Messaggi: 29309
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
Contatta:

IMA 2020-056 = princivalleite

Messaggio da Marco E. Ciriotti » ven 14 gen, 2022 20:22

Prossima pubblicazione.

Referenza:
▪ Bosi, F., Pezzotta, F., Skogby, H., Altieri, A., Hålenius, U., Tempesta, G., Cempírek, J. (2022): Princivalleite, Na(Mn2Al)Al6(Si6O18)(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup from Veddasca Valley (Varese, Italy). Mineralogical Magazine, 86, (in press).

Abstract:
Princivalleite, Na(Mn2Al)Al6(Si6O18)(BO3)3(OH)3O, is a new mineral of the tourmaline supergroup. It occurs in the Veddasca Valley, Luino area (Varese, Lombardy, Italy) (46°03’30.74’’N – 8°48’24.47’’E) at the center of a narrow (2-3 cm wide) vertical pegmatitic vein, a few meters long, crosscutting a lens of flaser gneiss. Crystals are subhedral (up to 10 mm in size), azure with a vitreous luster, conchoidal fracture and white streak. Princivalleite has a Mohs hardness of approximately 7, a calculated density of 3.168 g/cm3 and is uniaxial negative. Princivalleite has trigonal symmetry, space group R3m, a = 15.9155(2) Å, c = 7.11660(10) Å, V = 1561.15(4) Å3, Z = 3. The crystal structure was refined to R1 = 1.36 % using 1758 unique reflections collected with MoKα X-ray intensity data. Crystal-chemical analysis resulted in the empirical crystal-chemical formula X(Na0.54Ca0.110.35)Σ1.00Y(Al1.82Mn2+0.84Fe2+0.19Zn0.07Li0.08)Σ3.00Z(Al5.85Fe2+0.13Mg0.02)Σ6.00 [T(Si5.60Al0.40)Σ6.00O18](BO3)3 O(3)[(OH)2.71O0.29]Σ3.00 O(1)[O0.66F0.22(OH)0.12]Σ1.00 which recast in its ordered form for classification purposes is: X(Na0.54Ca0.110.35)Σ1.00Y(Al1.67Mn2+0.84Fe2+0.32Zn0.07Mg0.02Li0.08)Σ3.00ZAl6.00T[(Si5.60Al0.40)Σ6.00O18(BO3)3[(OH)2.71O0.29]Σ3.00W[O0.66F0.22(OH)0.12]Σ1.00. Princivalleite is an oxy-species belonging to the alkali group of the tourmaline supergroup. The closest end-member compositions of valid tourmaline species are those of oxy-schorl and darrellhenryite, to which princivalleite is related by the substitutions Mn2+ ↔ Fe2+ and Mn2+ ↔ 0.5Al3+ + 0.5Li+ (respectively). The new mineral was approved by the International Mineralogical Association’s Commission on New Minerals, Nomenclature and Classification (IMA 2020-056). Princivalleite from Veddasca Valley is a geochemical anomaly, originated in a B-rich and peraluminous anatectic pegmatitic melt formed in situ, poor in Fe and characterized by reducing conditions in the late-stage metamorphic fluids derived by the flaser gneiss. The Mn-enrichment in this new tourmaline is due to absence of other minerals competing for Mn such as garnet.
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