Sharyginite, Ca3TiFe2O8, A New Mineral from the Bellerberg Volcano, Germany.

Juroszek, Rafał; Krüger, Hannes; Galuskina, Irina; Krüger, Biljana; Jeżak, Lidia; Ternes, Bernd; Wojdyla, Justyna; Krzykawski, Tomasz; Pautov, Leonid; Galuskin, Evgeny

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.

GERMANY; IRON oxides; VOLCANOLOGY; PEROVSKITE; CARBONATES; EMPIRICAL research

Minerals (2075-163X), 2018, Vol 8, Issue 7, p308

2075-163X

Academic Journal

10.3390/min8070308