Reznitskyite, CaMg(VO4)F, a new mineral from the Tolbachik volcano, Kamchatka, Russia and the first vanadate with a titanite-type structure

Reznitskyite, ideally CaMg(VO4)F, is a new mineral species of the tilasite group from the Arsenatnaya fumarole, Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It occurs as zones (usually up to 0.05 mm thick) in crystals of V- and P-containing tilasite or as homogeneous grains up to 0.1 mm across. It was found in polymineralic sublimate encrustations in association with minerals of the svabite-fluorapatite-pliniusite system and the schaferite-berzeliite, tilasite-isokite, wagnerite-arsenowagnerite and udinaite-arsenudinaite series. The mineral assemblage also includes calciojohillerite, diopside, forsterite, titanite, rhabdoborite-(V), rhabdoborite-(W), rhabdoborite-(Mo), ludwigite, powellite, scheelite, hematite, baryte and magnesioferrite. Reznitskyite is transparent or semi-transparent, colourless, with vitreous lustre. D-ca(lc) = 3A53 g cm(-3). Under the microscope, in reflected light reznitskyite is grey, non-pleochroic, with very weak bireflectance (Delta R-589 (nm) = 0.5%) and distinct anisotropy. Reznitskyite is the first vanadate with a titanite-type structure. It is monoclinic, space group C2/c, a = 6.6912(7), b = 8.9395(7), c = 7.0587(8) angstrom, beta = 113.078(13)degrees, V = 388.43(8) angstrom(3) and Z = 4. The strongest reflections of the powder X-ray diffraction pattern are [d in angstrom(I)(hkl)]: 3.082(100)(200), 3.250 (66)((1) over bar 12, 002), 2.631(44)(022), 2.854(34)((2) over bar 02), 2.683(33)(130), 3.686(26)(021), 2.531(25)(220), 1.749(25)((3) over bar 32, (2) over bar 04) and 2.344(24)(131). Electron microprobe analysis gave (wt.%) MgO 20.44, CaO 26.83, P(2)O(5 )6.24, V2O5 21.09, As2O5 18.97, SO3 0.47, F 9.42, -O=F -3.97, with a total of 99.49. The empirical formula of reznitskyite, calculated on the basis of O+F = 5 atoms per formula unit, is: Ca0.97Mg1.03(V0.47As0.33P0.18S0.01)(Sigma 0.)99O3.99F1.01. Reznitskyite is a vanadate analogue of tilasite CaMg(AsO4)F and isokite CaMg(PO4)F. The mineral is named in honour of the outstanding Russian mineralogist Leonid Zinovievich Reznitsky (born 1938) who has made significant contribution to the mineralogy of vanadium.

Automated summary

Reznitskyite is a new mineral species discovered in Arsenatnaya fumarole of Tolbachik volcano, Russia. It has a unique crystal structure and chemical composition, and is found in association with other minerals.