IMA 2018-006a = ognitite

database, nuove specie, discrediti,
ridefinizioni, classificazioni, ecc.
Avatar utente
Marco E. Ciriotti
Messaggi: 25920
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy

IMA 2018-006a = ognitite

Messaggio da Marco E. Ciriotti » mer 08 mag, 2019 16:45

Prossima pubblicazione.

▪ Barkov, A.Y., Bindi, L., Tamura, N., Shvedov, G.I., Winkler,, B., Stan, C.V., Morgenroth, W., Martin, R.F., Zaccarini, F., Stanley, C.J. (2019): Ognitite, NiBiTe, a new mineral species, and cobaltian maucherite from the Ognit ultramafic complex, Eastern Sayans, Russia. Mineralogical Magazine, 83, (in press).

We describe the new species ognitite, NiBiTe, and a cobaltian variety of maucherite, hitherto unreported; both were discovered in the Ognit ultramafic complex of Neoproterozoic age in Eastern Sayans, Russia. The mean composition of ognitite (n = 7) is: Ni 17.05, Fe 0.07, Cu 0.14, Pd 0.14, Te 32.53, Bi 49.64, total 99.57 wt.%, corresponding to: (Ni1.11Cu<0.01Fe<0.01Pd<0.01)Σ1.13Bi0.90Te0.97 (Σ atoms = 3 apfu). Ognitite is trigonal, space group P3m1 [R1 = 0.0276 for 81 reflections with Fo > 4σ(Fo)]. The unit-cell parameters derived from the single-crystal X-ray diffraction data are: a = 3.928(1) Å, c = 5.385(1) Å, V = 71.95(4) Å3, with Z = 1. The c:a ratio is 1.37. The X-ray powder-diffraction data obtained on the same fragment used for the single-crystal study are: a = 3.9332(4) Å, c = 5.3920(6) Å, V = 72.24 (1) Å3. Ognitite exhibits the brucite-type structure with edge-sharing NiTe3Bi3 octahedra forming sheets parallel to (0001). It is related to melonite, but is distinct compositionally (by the extreme Bi-enrichment; melonite and its synthetic analogue contain <0.4 Bi apfu) and structurally: Bi and Te are ordered at two distinct sites, leading to the loss of the center of symmetry in ognitite. At more than 9 wt.% Co, or ~2 apfu Co, the core of cobaltian maucherite [(Ni,Co)11As8] in a zoned crystal, which is surrounded by Co-depleted orcelite, far surpasses the norm (≤1 and up to 3.9 wt.% Co). The unit-cell parameters of the Co-rich maucherite are: a = 6.85(2) and c = 21.83(5) Å, which are based on results of synchrotron micro-Laue diffraction. The host rock consists of serpentine, clinochlore (Mg# 95–97) and skeletal chromite. We favor the metastable crystallization of fluid saturated globules of a sulfide-arsenide melt to explain the anomalous compositions of ore minerals at Ognit. These anomalies seem consistent with rapid cooling in a fluid-enriched system, possibly related to late-stage degassing of the magma, as reflected in a prominent metasomatic aureole at the contact with the enclosing gneissic rocks.
Marco E. Ciriotti

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


Chi c’è in linea

Visitano il forum: Google [Bot] e 4 ospiti