IMA 2017-014 = sharyginite

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Marco E. Ciriotti
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IMA 2017-014 = sharyginite

Messaggio da Marco E. Ciriotti » dom 22 lug, 2018 11:01

Referenza:
▪ Juroszek, R., Krüger, H., Galuskina, I., Krüger, B., Jeżak, L., Ternes, B., Wojdyla, J., Krzykawski, T., Pautov, L., Galuskin, E. (2018): Sharyginite, Ca3TiFe2O8, A New Mineral from the Bellerberg Volcano, Germany. Minerals, 8, 308; doi.org/10.3390/min8070308.

Abstract
The new mineral sharyginite, Ca3TiFe2O8 (P21ma, Z = 2, a = 5.423(2) Å, b = 11.150(8) Å, c = 5.528(2) Å, V = 334.3(3) Å3), a member of the anion deficient perovskite group, was discovered in metacarbonate xenoliths in alkali basalt from the Caspar quarry, Bellerberg volcano, Eifel, Germany. In the holotype specimen, sharyginite is widespread in the contact zone of xenolith with alkali basalt. Sharyginite is associated with fluorellestadite, cuspidine, brownmillerite, rondorfite, larnite and minerals of the chlormayenite-wadalite series. The mineral usually forms flat crystals up to 100 µm in length, which are formed by pinacoids {100}, {010} and {001}. Crystals are flattened on (010). Sharyginite is dark brown, opaque with a brown streak and has a sub-metallic lustre. In reflected light, it is light grey and exhibits rare yellowish-brown internal reflections. The calculated density of sharyginite is 3.943 g·cm-3. The empirical formula calculated on the basis of 8 O apfu is Ca3.00(Fe3+1.00Ti4+0.86Mn4+0.11Zr0.01Cr3+0.01Mg0.01)Σ2(Fe3+0.76Al0.20Si0.04)Σ1.00O8. The crystal structure of sharyginite, closely related to shulamitite Ca3TiFeAlO8 structure, consists of double layers of corner-sharing (Ti, Fe3+) O6 octahedra, which are separated by single layers of (Fe3+O4) tetrahedra. We suggest that sharyginite formed after perovskite at high-temperature conditions >1000°C.

NdR: La specie, l-analogo Fe3+ della shulamitite, è parte del sottogruppo brownmillerite (gruppo defect oxide perovskite A2BTX5; supergruppo perovskite; famiglia non-stoichiometric perovskites anion deficient perovskites)

Brownmillerite Ca2(Fe3+Al)O5 orth Ibm2 5.567 14.521 5.349 90.00 90.00 90.00
Sharyginite Ca3(Ti4+Fe3+)Fe3+O8 orth P21ma 5.423 11.150 5.528 90.00 90.00 90.00
Shulamitite Ca3(Ti4+Fe3+)AlO8 orth Pmma 5.4200 11.064 5.5383 90.00 90.00 90.00
Srebrodolskite Ca2(Fe3+Fe3+)O5 orth Pcmn 5.420 14.752 5.594 90.00 90.00 90.00
Marco E. Ciriotti

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