Fluoroleakeite, NaNa2(Mg2Fe23+Li)Si8O22F2, a new mineral of the amphibole group from the Verkhnee Espe deposit, Akjailyautas Mountains, Eastern Kazakhstan District, Kazakhstan: description and crystal structure

Fluoroleakeite. NaNa2(Mg2Fe23+L1)Si8O22F2, is a new mineral of the amphibole group from the Verkhnee Espe deposit, Akjailyautas mountains, eastern Kazakhstan district, Kazakhstan The granites and their host rocks have been intensely reworked by post-magmatic and host-rock fluids. resulting in intense recrystallization. enrichrnent in F, L1 and rate elements, and replacement of primal), biotite and sodic-calcic amphiboles by Li-bearing riebeckite. aegurine, astrophyllite and other sodic minerals including flouroleakene Crystals are prismatic parallel to [001] with 11001 and;110; faces and cleavage surfaces. and the prism direction is terminated by irregular fractures Owns are up to 3 mm long. and occur as isolated crystals, as small aggregates. and as inclusions in camaraite Crystals ate black with a very pale grey to colourless streak Fluroleakeite Is brittle, has a Mobs hardness of 6 and a splintery fracture. it is non-fluorescent with perfect {1 10} cleavaee, no observable parting, and has a calculated density of 3 245 e cm(-3) In plane-polarized light. It IS pleochronic, = pale grey-green, Y = medium grey, Z = grey-brown. X boolean AND a = 14 1 degrees (in beta obtuse). Y vertical bar vertical bar b. ZAc = 75 9 degrees (m beta acute) Fluoroleakeite is biaxial negative, a = 1 663(2), beta = I 673(2), gamma = 1 680(2), 2V(obs) = 80 9(6)degrees, 2V(calc) = 79 4 degrees Fluoro-leakeite is monoclinic, space group C2/m, a = 9 8927(3), b = 17 9257(6), c = 5 2969(2) A. 13 = 103 990(1)degrees V = 905 7(1) angstrom(3.) Z = 2 The strongest ten X-ray diffraction lines in the powder pattern are [d angstrom(I)(hkl)] 2 718(100)(151). 8 434(40)(110), 4 464(30)(021). 3 405(30)(131), 3 137(20)(3 I 0), 2 541(20)(02), 2 166(20)(261), 2.325(15)(351), 2 275(15)(112) and 2 806(10)(330) Analysis by a combination of electron microprobe and crystal-structure refinement gives SiO2 53 34, Al2O3 0 62, TiO2 1 27, V2O3 0 05 Fe2O3 15 10 FEO 6 00 MnO 204. ZnO 0 18. MgO 640, CaO 0 13. Na2O 908. K2O 1 98 Li2O 1.10, F 3.33 H2Ocale 0.16 sum 99 39 wt% The formula unit, calculated on the basis of 23 O is (A)(Na0 64K0 98)Na1 98Ca0 02)Li(0 66)Mg(1 42)Fe(0 75)(2+)Mn(0 26)(2+)Zn(0 02)Fe(1 69)(3+)V(0 01)(3+)Ti(0 14)(4+)Ai(0 03)) (SI(7 93)AI(0 07))O-22(F1 57OH0 16O0 27) Crystal-structure refinement shows Li to be completely ordered at the M(3) site. Fluoroleakene. ideal ly NaNa2(Mg2Fe23+Li)S18O22F2. is related to end-member leakeite. NaNa2(Mg2Fe23+Li)Si8O22(OH)(2) by the substitution F -> (OH)