Elbrusite-(Zr); a new uranian garnet from the Upper Chegem Caldera, Kabardino-Balkaria, Northern Caucasus, Russia

• Published in: The American mineralogist Vol. 95; no. 8-9; pp. 1172 - 1181
• Main Authors: Galuskina, Irina O, Galuskin, Evgeny V, Armbruster, Thomas, Lazic, Biljana, Kusz, Joachim, Dzierżanowski, Piotr, Gazeev, Viktor M, Pertsev, Nikolai N, Prusik, Krystian, Zadov, Aleksandr E, Winiarski, Antoni, Wrzalik, Roman, Gurbanov, Anatoly G
• Format: Journal Article
• Language: English
• Published: Washington Mineralogical Society of America 01.08.2010; De Gruyter; Walter de Gruyter GmbH
• Subjects: actinides; Atoms & subatomic particles; Calderas; Caucasus; color; Commonwealth of Independent States; crystal chemistry; crystal structure; Crystals; EBSD; elbrusite; Elbrusite-(Zr); electron diffraction data; Europe; formula; garnet group; inclusions; Kabardin-Balkar Russian Federation; metals; metamictization; metamorphic rocks; metasomatic rocks; Mineralogy; Minerals; nesosilicates; new garnet; new minerals; Northern Caucasus; orthosilicates; Perovskite; Raman spectra; Raman spectroscopy; Russian Federation; silicates; skarn; solid solution; space groups; spectra; Upper Chegem Caldera; Uranium; volcanic features; X-ray diffraction data; xenoliths; zirconium; Caucasus
• ISSN: 0003-004X; 1945-3027
• DOI: 10.2138/am.2010.3507

Elbrusite-(Zr) Ca3(U6+Zr)(Fe3+2Fe2+)O12, a new uranian garnet (Ia3d, a≈12.55 Å, V≈1977 Å3, Z=8), within the complex solid solution elbrusite-kimzeyite-toturite Ca3(U,Zr,Sn,Ti,Sb,Sc,Nb...)2(Fe,Al,Si,Ti)3O12 was discovered in spurrite zones in skarn xenoliths of the Upper Chegem caldera. The empirical formula of holotype elbrusite-(Zr) with 25.14 wt% UO3 is (Ca3.040 Th0.018 Y0.001)Σ3.059(U6+0.658 Zr1.040 Sn0.230 Hf0.009 Mg0.004)Σ1.941(Fe3+1.575 Fe2+0.559 Al0.539 Ti4+0.199 Si0.099 Sn0.025 V5+0.004)Σ3O12. Associated minerals are spurrite, rondorfite, wadalite, kimzeyite, perovskite, lakargiite, ellestadite-(OH), hillebrandite, afwillite, hydrocalumite, ettringite group minerals, and hydrogrossular. Elbrusite-(Zr) forms grains up to 10-15 µm in size with dominant {110} and minor {211} forms. It often occurs as zones and spots within Fe3+-dominant kimzeyite crystals up to 20-30 µm in size. The mineral is dark-brown to black with a brown streak. The density calculated on the basis of the empirical formula is 4.801 g/cm3 The following broad bands are observed in the Raman spectra of elbrusite-(Zr): 730, 478, 273, 222, and 135 cm-1. Elbrusite-(Zr) is radioactive and nearly completely metamict. The calculated cumulative dose (α-decay events/mg) of the studied garnets varies from 2.50×1014 [is equivalent to 0.04 displacement per atom (dpa)] for uranian kimzeyite (3.36 wt% UO3), up to 2.05×1015 (0.40 dpa) for elbrusite-(Zr) with 27.09 wt% UO3.