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, P1, a = 7.0477(5), b = 9.8725(5), c = 12.2204(9) Å, α = 77.995(5), β = 82.057(6), γ = 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°40’, E 33°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 (–), α 1.670(2), β 1.690(2), γ 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)∑13.10(Fe0.72Mn0.69□0.54Mg0.05)∑2.00 (Ti1.81Nb0.19)∑2.00(Zr2.27Ti0.63)∑2.90(Si2O7)4{(OH)5.94O3.09F2.97}∑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.
Highlights
Zircono- and titanosilicates of the wöhlerite family are characteristic minerals of the alkaline complexes, including the Khibiny massif in Kola Peninsula, Russia
Minerals 2019, 9, 219 modular crystal structures formed by Si2 O7 groups and complex zigzag octahedral walls similar to those observed in borates with wallpaper structures [1,2]
Optical properties of chirvinskyite were determined by using an Amplival optical microscope (Carl Zeiss Microscopy, Jena, Germany) and standard immersion liquids
Summary
Zircono- and titanosilicates of the wöhlerite family are characteristic minerals of the alkaline complexes, including the Khibiny massif in Kola Peninsula, Russia. The chemical composition and configuration of these walls vary widely [3,4], which results in about 10 approved wöhlerite-related minerals, with five of them (wöhlerite, låvenite, normandite, cuspidine, and chirvinskyite) occuring in the Khibiny massif [5]. The thinnest split fibers of an unknown låvenite-like mineral were found by late Yuri Men’shikov (1934–2013) during an investigation of the apatite/molybdenite/parakeldyshite deposit at Mt. Takhtarvumchorr [5]. Men’shikov obtained chemical and powder XRD data for this mineral and proposed to name it in honor of Prof.
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