Elbrusite-(Zr) Ca 3 (U 6+ Zr)(Fe 3+ 2 Fe 2+ )O 12 , a new uranian garnet (Ia3̅d, a ≈ 12.55 Å, V ≈ 1977 Å 3 , Z = 8), within the complex solid solution elbrusite-kimzeyite-toturite Ca 3 (U,Zr,Sn,Ti,Sb,Sc,Nb...) 2 (Fe,Al,Si,Ti) 3 O 12 was discovered in spurrite zones in skarn xenoliths of the Upper Chegem caldera. The empirical formula of holotype elbrusite-(Zr) with 25.14 wt% UO 3 is (Ca 3.040 Th 0.018 Y 0.001 ) Σ3.059 (U 6+ 0.658 Zr 1.040 Sn 0.230 Hf 0.009 Mg 0.004 ) Σ1.941 (Fe 3+ 1.575 Fe 2+ 0.559 Al 0.539 Ti 4 0.199 Si 0.099 Sn 0.025 V 5+ 0.004 ) Σ3 O 12 . 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 Fe 3+ -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/cm 3 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 × 10 14 [is equivalent to 0.04 displacement per atom (dpa)] for uranian kimzeyite (3.36 wt% UO 3 ), up to 2.05 × 10 15 (0.40 dpa) for elbrusite-(Zr) with 27.09 wt% UO 3 .
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Galuskina et al. (2010) studied this question.