Chirvinskyite, (Na,Ca)13(Fe,Mn,)2(Ti,Nb)2(Zr,Ti)3-(Si2O7)4(OH,O,F)12, a New Mineral with a Modular Wallpaper Structure, from the Khibiny Alkaline Massif (Kola Peninsula, Russia)

Chirvinskyite, (Na,Ca)(13)(Fe,Mn,)(2)(Ti,Nb)(2)(Zr,Ti)(3)(Si2O7)(4)(OH,O,F)(12), is a new wohlerite-related zirconotitano-sorosilicate. It is triclinic, P a = 7.0477(5), b = 9.8725(5), c = 12.2204(9) angstrom, = 77.995(5), = 82.057(6), = 89.988(5)degrees, V = 823.35(9) angstrom(3), Z = 1. The mineral was found in albitized alkaline pegmatites in a foyaite of the Mt. Takhtarvumchorr (Khibiny alkaline massif, Kola Peninsula, Russia, N 67 degrees 40, E 33 degrees 33). Chirvinskyite forms sheaf-like and radiated aggregates (up to 6 mm in diameter) of split fibrous crystals hosted by saccharoidal fluorapatite and albite. The mineral is pale cream in color, with a silky luster and a white streak. The cleavage is not recognized. Mohs hardness is 5. Chirvinskyite is biaxial (-), 1.670(2), 1.690(2), 1.705(2) (589 nm), 2V(calc) = 80.9 degrees. The calculated and measured densities are 3.41 and 3.07(2) gcm(-3), respectively. The empirical formula based on Si = 8 apfu is (Na9.81Ca3.28K0.01)(Sigma 13.10)(Fe0.72Mn0.690.54Mg0.05)(Sigma 2.00) (Ti1.81Nb0.19)(Sigma 2.00)(Zr2.27Ti0.63)Sigma 2.90(Si2O7)(4){(OH)(5.94)O3.09F2.97}(Sigma 12.00). Chirvinskyite belongs to a new structure type of minerals and inorganic compounds and is related to the wohlerite-group minerals. Its modular wallpaper structure consists of disilicate groups Si2O7 and three types of octahedral walls. The mineral is named in honor of Petr Nikolaevich Chirvinsky (1880-1955), Russian geologist and petrographer, head of the Petrography Department of the Perm' State University (1943-1953), for his contributions to mineralogy and petrology, including studies of the Khibiny alkaline massif.