Moxuanxueite, NaCa6Zr(Si2O7)2OF3, a new wöhlerite-group mineral from Gejiu alkaline complex, Yunnan Province, China

Abstract Moxuanxueite, ideally NaCa6Zr(Si2O7)2OF3, is a new wöhlerite-group mineral that we report in this study from the Gejiu alkaline complex, Yunnan Province, China. This new species occurs as subhedral to euhedral polysynthetic twinned grains, and as elongate crystals up to 1 mm in size, commonly associated with tiny baddeleyite at the grain margins and usually associated with calcioancylite-(La), bobtraillite, catapleiite, fluorite, and jadeite. Moxuanxueite is light yellow in color with metallic luster. It is very brittle with conchoidal fracture and has a calculated density of 3.231 g/cm3. The empirical formula calculated on the basis of O + F = 18 apfu is Na1.38Ca5.21Fe0.23Mn0.22(Zr0.88Ti0.14)Σ1.02(Si2.01O7)2(F3.15O0.85)Σ4.00. The ideal formula requires (wt.%) Na2O 4.06, CaO 44.04, ZrO2 16.13, SiO2 31.46, F 7.46, O≡F -3.14, and a total of 100 wt.%. The mineral is triclinic, with space group P1¯ (#2), a = 11.0235(3) Å, b = 10.9641(4) Å, c = 7.3805(4) Å, α = 109.523(2)°, β = 109.881(2)°, γ = 83.434(2)°, V = 790.63(6) Å3, and Z = 2. The seven strongest X-ray powder diffraction lines [d in Å (I) (hkl)] are: 3.005 (100) (1¯12), 2.870 (57) (230), 1.849 (32) (2¯2¯4), 10.42 (30) (1¯00), 2.496 (26) (14¯0), 3.280 (23) (3¯1¯0), and 1.701 (20) (16¯2). Moxuanxueite is isostructural with hiortdahlite [Na2Ca4(Zr0.5Ca0.5)(Si2O7)2OF3], and the transformation between the two phases is via the following substitution mechanism to keep charge balance: 2Ca2+ ⇋ Na+ + 0.5Zr4++0.5Ca2+ . The new mineral is named in honor of Professor Xuanxue Mo (born 1938), a distinguished petrologist from the China University of Geosciences (Beijing), for his outstanding contribution to magmatism and related mineralization in China.