Cámaraite, Ba₃NaTi₄(Fe²⁺,Mn)₈(Si₂O₇)₄O₄(OH,F)₇. I. A new Ti-silicate mineral from the Verkhnee Espe Deposit, Akjailyautas Mountains, Kazakhstan

Abstract

OH,F) 7 , is a new mineral from the Verkhnee Espe deposit, Akjailyautas Mountains, Kazakhstan. It occurs as intergrowths with bafertisite and jinshajiangite in separate platy crystals up to 8 mm615 mm62 mm in size, or as star-shaped aggregates of crystals with different orientations. Individual crystals are orange-red to brownish-red, and are platy on {001}. Cámaraite is translucent and has a pale-yellow streak, a vitreous lustre, and does not fluoresce under cathode or ultraviolet light. Cleavage is {001} perfect, no parting was observed, and Mohs hardness is <5; the mineral is brittle. The calculated density is 4.018 g cm À3 . In transmitted light, cámaraite is strongly pleochroic, X = light brown, Y = reddish-brown, Z = yellowbrown, with Z < X < Y. Cámaraite is biaxial +ve and 2V meas. = 93(1)º. All refractive indices are greater than 1.80. Cámaraite is triclinic, space group C1, a = 10.678 (4) Å , b = 13.744(8) Å , c = 21.40(2) Å , a = 99.28(8)º, b = 92.38(5)º, g = 90.00(6)º, V = 3096(3) Å 3 , Z = 4, a:b:c = 0.7761:1:1.5565. The seven strongest lines in the X-ray powder-diffraction pattern are as follows: [d (99.63 wt.%, where the valence state of Fe was determined by Mössbauer spectroscopy [Fe 3+ /(Fe 2+ + Fe 3+ ) = 0.13(8)] and the H 2 O content was derived by crystal-structure determination. The resulting empirical formula on the basis of 39 anions is

Petrology of combeite- and götzenite-bearing nephelinite at Nyiragongo, Virunga Volcanic Province in the East African Rift

“…Open circles: Analyses from the present study (Table 10b in Supplementary data), black spot: Average of these. Grey circles, theoretical compositions of bafertisite-group minerals (Sokolova, 2006;Sokolova et al, 2009 trace components Nb and REE can be disregarded without serious consequences for the analysis. Zr is a minor component in götzenite, substituting for Ti, but no separate Zr mineral has been observed in this study or in any of the previous studies of the Nyiragongo nephelinites; Zr can therefore be assumed to behave as a minor substituent for Ti.…”

Ferri-fluoro-leakeite: a second occurrence at Bratthagen (Norway), with new data on Zn partitioning and the oxo component in Na amphiboles

“…The EMPA and crystal structure refinement showed that it is ferrifluoro-leakeite (Hawthorne et al, 2012), a mineral species described by Cámara et al (2010) from the Verkhnee Espe deposit (Kazakhstan) under the name (in force at that time) of ''fluoroleakeite''. The Verkhnee Espe deposit is an intrusion of alkali granite in the northern exocontact of the Akjailyantas granite massif; it is the type locality of six species: bastnaesite-(Y), gagarinite-(Y), cámaraite, natrotitanite, tarbagataite and ferri-fluoro-leakeite (Stepanov and Sverov, 1961;Mineev et al, 1970;Sokolova et al, 2009;Cámara et al, 2010;Stepanov et al, 2012a,b). Both the difference in petro-genetic conditions and in chemical composition with respect to holotype ferri-fluoro-leakeite provide significant new information on the genesis and crystal-chemistry of C Li amphiboles and the longrange order of some exotic cations (i.e.…”

Cámaraite, Ba3NaTi4(Fe2+,Mn)8(Si2O7)4O4(OH,F)7. II. The crystal structure and crystal chemistry of a new group-II Ti-disilicate mineral

“…CAmaraite from the Verkhnee Espe deposit, A kjailyautas M ountains, K azakhstan, was described as a new mineral by Sokolova et al (2009a). Their chemical analysis by electron microprobe gave: Nb20 5 1.57, S i0 2 25.25, T i0 2 15.69, Z r0 2 0.33, Al20 3 0.13, Fe20 3 2.…”

“…77, FeO 16.54, MnO 9.46, ZnO 0.12, MgO 0.21, CaO # 2009 The Mineralogical Society 0.56, BaO 21.11, Na2O 1.41, K2O 0.84, H2O 1.84, F 3.11, less O : F 1.31, total 99.63 wt.%, where the valence states of Fe were determined by Mossbauer spectroscopy [Fe3+/(Fe2+ + Fe3+) = 0.13(8)] and the H2O content was derived by crystal-structure determination (the latter issue is discussed further in this paper). Sokolova et al (2009a) gave the following em pirical and simplified formulae: (Ba2.61K0.34)S2.95(Na0.86Ca0.14)S1 (Ti3.72Nb0.22Al0.05)S3.99(Fe4.36Fe0.66Mn2.53Mg0.10 Zr0.05Zn0.03Ca0.05)E7.78Si7.97O35.89H3.88F3.n, and Ba3NaTi4(Fe2+,Mn)8(Si2O7)4O4(OH,F)7, Z = 4, on the anion basis F + O + OH = 39 a.p.f.u. (atoms per formula unit), Dcalc.…”

“…respectively. Based on the Ti content, Sokolova et al (2009a) considered camaraite as a Group-II mineral, i.e. Ti = 2 a.p.f.u.…”