Structure refinement and crystal chemistry of tokkoite and tinaksite from the Murun massif (Russia)

Abstract

The structures of tokkoite, K2Ca4[Si7O18OH](OH,F) and tinaksite, K2Ca2NaTi[Si7O18OH]O from the Murun massif (Russia) were refined from single-crystal X-ray diffraction data in the triclinic space group P 1: Average crystallographic data are a≈10.423, b≈12.477, c≈7.112 Å, α≈89.92°, β≈99.68°, γ≈92.97°, V≈910.5 Å3 for tokkoite; a≈10.373, b≈12.176, c≈7.057 Å, α≈90.82°, β≈99.22°, γ≈ 92.80°, V≈878.5 Å3 for tinaksite. The substantial similarities between the geometrical parameters of the tokkoite and tinaksite structures led us to conclude that the two minerals are isostructural. However, major differences of tokkoite with respect to tinaksite are larger lattice constants, especially concerning the b parameter, longer <M–O> distances, especially <M1–O>; larger values of the M1–M3 and O20–O2 bond lengths, and a stronger distortion of the M1 polyhedron. Mössbauer analysis showed that significant trivalent iron is present, VIFe3+ 40.0(7)% in tokkoite and 12.8(3)% in tinaksite. It is confirmed that 2Ca2þ (M1þM2) +(F, OH)(O20) ↔ Ti4þ (M1) +Naþ(M2) +O(O20) is the exchange reaction that describes the relation between tokkoite and tinaksite. In addition, this exchange reaction causes local stress involving mainly the M1 site and its interaction with the M2 and M3 sites

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

“…It is reasonable to start the description of the crystal structure of fluorcarletonite from silicate layers. According to Liebau (2012), the loop-branched sechser doublesilicate layer in carletonite, as well as in fluorcarletonite (Fig. 5a), results from the condensation of two branched single layers (Fig.…”

“…(Cannillo et al, 1969;Pekov et al, 2009); rhodesite, KNa 2 Ca 2 Si 8 O 19 (OH) • 6H 2 O (Hesse and Liebau, 1992); macdonaldite, BaCa 4 Si 16 O 36 (OH) 2 • 10H 2 O (Cannillo et al, 1968); and monteregianite-(Y), Na 4 K 2 Y 2 Si 16 O 38 • 10H 2 O (Ghose et al, 1987) (Table S5, Supplement S1). However, all these silicates have branched dreier double layers [(Si, Al) 8 O 19 ] of the same topology (Liebau, 2012), whereas fluorcarletonite and carletonite contain [Si 8 O 18 ] layers. Two independent silicate tetrahedra of the single layer form eight-membered rings connected by four-membered rings with four adjacent eight-membered rings.…”

“…Fluorcarletonite, idealized KNa 4 Ca 4 Si 8 O 18 (CO 3 ) 4 F q H 2 O, is the rare mineral belonging to the group of phyllosilicates. The crystal structure contains infinite branched sechser double-silicate layers (Liebau, 2012) composed of interconnected four-and eight-membered rings of SiO 4 tetrahedra and connected through the sheets of interlayer K-, Na-and Ca-centered polyhedra and CO 3 triangles. Fluorcarletonite is an F analogue of carletonite, discovered in 1971 by Chao and named after the Carleton University (Chao, 1971).…”

40Ar/39Ar Geochronology of the Malyy (Little) Murun Massif, Aldan Shield of the Siberian Craton: A Simple Story for an Intricate Igneous Complex

“…The Malyy Murun has a high potential for mineralogists and petrologists. It is worth mentioning that a number of new minerals and mineral varieties have been discovered there (charoite [20,25], tinaksite [26,27], tokkoite [27,28], frankamenite [29,30], strontian potassicrichrerite [31,32], tausonite [33,34], murunskite [35,36], vladykinite [37]), and various exotic rocks such as lamproites, carbonatites, alkaline granites, and various syenitic rocks.…”

⁴⁰Ar/³⁹Ar Geochronology of the Malyy (Little) Murun Massif, Aldan Shield of the Siberian Craton: A Simple Story for an Intricate Igneous Complex

“…The Malyy Murun has high potential for mineralogists and petrologists. Worth to mention a number of new minerals and mineral varieties discovered there (charoite [20,25], tinaksite [26][27], tokkoite [27][28], frankamenite [29][30], strontian potassicrichrerite [31][32], tausonite [33][34], murunskite [35][36], vladykinite [37]) and various exotic rocks such as lamproites, carbonatites, alkaline granites and various syenitic rocks.…”