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)

Abstract

Chirvinskyite, (Na,Ca)13(Fe,Mn, )2(Ti,Nb)2(Zr,Ti)3(Si2O7)4(OH,O,F)12, is a new wöhlerite– related zirconotitano–sorosilicate. It is triclinic, P 1, a = 7.0477(5), b = 9.8725(5), c = 12.2204(9) Å, = 77.995(5), = 82.057(6), = 89.988(5) , V = 823.35(9) Å3, Z = 1. The mineral was found in albitized alkaline pegmatites in a foyaite of the Mt. Takhtarvumchorr (Khibiny alkaline massif, Kola Peninsula, Russia, N 67 400, E 33 330). 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), 2Vcalc = 80.9 . The calculated and measured densities are 3.41 and 3.07(2) g cm􀀀3, respectively. The empirical formula based on Si = 8 apfu is (Na9.81Ca3.28K0.01)P 13.10(Fe0.72Mn0.69 0.54Mg0.05)P 2.00 (Ti1.81Nb0.19)P 2.00(Zr2.27Ti0.63)P 2.90(Si2O7)4{(OH)5.94O3.09F2.97}P 12.00. Chirvinskyite belongs to a new structure type of minerals and inorganic compounds and is related to the wöhlerite-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.