Koksharovite, CaMg2Fe3+4(VO4)6, and grigorievite, Cu3Fe3+ 2Al2(VO4)6, two new howardevansite-group minerals from volcanic exhalations
Two new howardevansite-group minerals were discovered in the exhalations of fumaroles related to two volcanoes in Kamchatka, Russia. Koksharovite, CaMg2Fe 3þ 4(VO4)6, is found at the Bezymyannyi volcano in association with bannermanite. Grigorievite, Cu3Fe 3þ 2Al2(VO4)6, associated with bannermanite, ziesite, hematite, etc., was found at the Second scoria cone of the NorthernBreakthroughoftheGreatTolbachikFissureEruption,Tolbachikvolcano.Koksharoviteoccursasequanttoprismaticcrystals upto30 � 70mm.Itistranslucent,yellowish-browntoreddish-brownwithanadamantinelustre.Grigorieviteformsprismatic totabular crystals up to 40 � 100 mm. It is opaque, black with a semi-metallic lustre. Both minerals are brittle. The VHN hardness is 368 and 489 kg mm � 2 , the calculated density (Dcalc) 3.39 and 3.67 g cm � 3 for koksharovite and grigorievite, respectively. In reflected light, koksharovite is light grey, grigorievite is grey; both minerals are weakly anisotropic. Reflectance values (koksharovite//grigorievite: Rmax-Rmin ,%( l, nm)) are: 15.3-14.4//16.8-16.4 (470), 14.1-13.2//15.9-15.5 (546), 13.8-13.0//15.3-14.9 (589), 13.4-12.7//14.8-14.1 (650). Chemical data (wt%, electron-microprobe analysis; first value is for koksharovite, second for grigorievite) are: Na2O 0.76, 0.00; K2O 0.05, 0.00; MgO 9.43,2.78; CaO 3.57, 0.95; MnO 0.46,0.04;CuO 0.00,17.70; NiO 0.11, 0.00;ZnO 0.00,0.14; Al2O3 3.04,11.76; Fe2O3 23.88, 10.10; TiO2 2.42, 1.47; SiO2 0.20, 0.00; P2O5 0.98, 0.13; V2O5 53.86, 54.97; total 98.76, 100.04. The empirical formulae, based on 24 O atoms per formula unit, are: Na0.24K0.01Ca0.63Mg2.30Mn0.06Ni0.01Al0.59Fe 3þ 2.94Ti0.30Si0.03P0.14V5.83O24 (koksharovite); Ca0.17Mg0.69Mn0.01Cu2.23Zn0.02Al2.31Fe 3þ 1.27Ti0.18P0.02V6.05O24(grigorievite).Bothmineralsaretriclinic,spacegroupP-1,Z ¼1.Unit-