Crystal chemistry of fluorcarletonite, a new mineral from the Murun alkaline complex (Russia)

Abstract

Abstract. This paper reports the first description of the crystal structure and crystal chemical features of fluorcarletonite, a new mineral from the Murun potassium alkaline complex (Russia), obtained by means of single-crystal and powder X-ray diffraction (XRD), electron microprobe analysis (EMPA), thermogravimetry (TG), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. The crystal structure of fluorcarletonite, KNa4Ca4Si8O18(CO3)4(F,OH)⚫ H2O, a rare phyllosilicate mineral, contains infinite double-silicate layers composed of interconnected four- and eight-membered rings of SiO4 tetrahedra and connected through the interlayer K-, Na- and Ca-centered polyhedra and CO3 triangles. The X-ray diffraction analysis confirms the mineral to be tetragonal, P4∕mbm, a=13.219(1) Å, c=16.707(2) Å, V=2919.4(6) Å3 (powder XRD data), a=13.1808(5) Å, c=16.6980(8) Å, V=2901.0(3) Å3 (single-crystal XRD data, 100 K). The EMPA (average from 10 analyses) gave the following composition (wt %): SiO2 44.1(6), CaO 20.0(3), Na2O 11.1(3), K2O 4.5(2), F 1.3(5), TiO2 0.1(1) and Al2O3 0.03(3). The TG–DSC analysis confirmed the presence of H2O and CO2 (weight losses of 1.17 % and 14.9 %, respectively). The FTIR spectrum acquired in the range from 4000 to 400 cm−1 reveals the presence of H2O, CO3 and OH groups. The average formula of fluorcarletonite calculated from the results of EMPA and crystal structure refinement is K1.04Na3.89Ca3.87Ti0.01Si7.99Al0.01O18(CO3)3.86(F0.72OH0.28)⚫1.11H2O.

Fedorite from Murun Alkaline Complex (Russia): Spectroscopy and Crystal Chemical Features

“…There are further six-and eight-membered rings with a size of ~5.49 × 5.34 and ~5.80 × 5.66 Å, respectively. These values are quite close to those found in other silicates from the Murun charoite-bearing rocks (see, for example, [32,[34][35][36]).…”

“…All tetrahedra evidence a notable shortening of unshared Si-O bond lengths (<Si-O unsh >~1.587 Å) with respect to shared ones (<Si-O sh >~1.621 Å). This feature is pronounced in the crystal structure of the structurally and chemically related silicate minerals from Murun massif (for instance, miserite [34], frankamenite [37], tinaksite and tokkoite [35], fluorcarletonite [36], agrellitte [32].…”

Structural and vibrational properties of agrellite

“…0.81 and 0.79 vu, respectively). A similar feature was recently pronounced in the crystal structure of fluorcarletonite 29 , a chemically related mineral from the Murun massif.…”

Tinaksite and Tokkoite: X-ray Powder Diffraction, Optical, and Vibrational Properties

“…Subsequently, tinaksite has been reported from the complex pegmatites of the Rasvumchorr deposit, Khibiny massif (Kola Peninsula, Russia) [3,4] and tokkoite has been found at the massif of Patyn Mt., Tashtagolskiy District (Southern Siberia, Russia) [5]. Tinaksite and tokkoite belong to the group of rare alkaline Ca-(K)-(Na) silicates, which also includes such minerals as agrellite ( [6] and therein), miserite ( [7] and therein), frankamenite ( [8] and therein), fluorcarletonite [9], fedorite ( [10] and therein), fluorapophyllite-(K) [11], pectolite ( [12] and therein), denisovite [13], and charoite ([14 -16] and therein).…”

“…Naturally occurring aggregates of chain silicate crystals and their synthesized analogs are well known in the production of bioactive ceramics for their strength and fracture resistance. The structural features of the minerals of this group of rare alkaline Ca-(K)-(Na) silicates make these materials promising for ion exchange, since, as noted in [6][7][8][9][10][11][12][13][14][15][16]18,19], the crystal structures contain several cationic positions suitable for doping with transition metals and lanthanides. Finally, materials activated with transition and rare earth elements are widely used in various fields of photonics.…”