LIU Jia-jun ^{1, 2}, LI Guo-wu ^{1, 2}, MAO Qian ³, WU Sheng-hua ^{1, 2}, LIU Zhen-jiang ^{1, 2}, SU Shang-guo ^{1, 2}, XIONG Ming ^{1, 2}, YU Xiao-yan ⁴

(1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences,Beijing 100083, China;
2. School of Earth Earth Science and Resources, China University of Geosciences,Beijing 100083, China;
3. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;
4. School of Gemology, China University of Geosciences,Beijing 100083, China)

Abstract: Hanjiangite, a new mineral for the ideal formula Ba2Ca(V3+Al)[Si3AlO10(OH)2]F(CO3)2, is found in the Shiti barium deposit in the Dabashan region, China. Hanjiangite was collected from lenticular witherite ore bodies and witherite-barite-quartz veins cutting carbonaceous slates. It is found as disseminations in both settings. It occurs as thin, euhedral, tetragonal, tabular crystals and anhedral grains. Grain size commonly varies from 0.05 to 4 mm and occasionally reaches 15 mm. It is yellow-green or dark-green, with one well-developed or perfect cleavage on {001}. Other physical properties are: brittle, transparent to translucent, nonfluorescent, vitreous luster, greenish white streak, hardness 4 in Mohs' scale, splintery fracture, and a measured density of 3.69 g/cm3. Hanjiangite is biaxial (–), α = 1.615, β = 1.655, γ = 1.700 (589 nm), displays strong pleochroism from pale yellow-green to dark green. It is monoclinic, with unit-cell parameters refined by using single-crystal X-ray diffraction: a = 5.2050(12), b = 9.033(2), c = 32.077(8) Å, β = 93.49(8)˚, V = 1505.4(8) Å3, Z = 4, space group C2. The strongest seven lines of the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are: 15.866(7)(002), 5.340(91)(006), 4.010(10)(1(_)14), 3.209(23) (027), 2.676(100) (1(_)110), 2.294(29)(1(_)37), and 2.008(11)(28). A single-crystal X-ray structure determination (sample 2005st-17) was carried out with a Smart APEX CCD system using MoKα ( λ = 0.71073 Å) radiation. The structure was solved using direct methods, and the refinement conducted with the SHELXTL PC (Bruker AXS Inc.) package of computer programs. Anisotropic refinement using all measured independent data and reflections with I > 2σ(I) resulted in an R1 factor of 0.08 and wR2 of 0.20. The crystal structure is composed of alternating T-O-T and Ba2Ca(CO3)2F layers. The Ba2Ca(CO3)2F layer occurs between the T-O-T layers. The T site contains both Si and Al,and the O site both V3+ and Al. The difference is observed in the interlayer, where instead of only Ba (like in chernykhite) there are also Ca atoms and (CO3) groups.Whereas the coordination of the cations in TOT layer are obvious; the coordinations of Ca and Ba in the interlayer are not obvious and not completely different. A hanjiangite has possibly three polytypes, namely 1M-type, 2M-type, and 3T-type.

Key words: new mineral; hanjiangite; chemical formula; crystal structure; Shiti barium deposit; southern Shanxi; China

E-mail: liujiajun@cugb.edu.cn

ACTA MINERALOGICA SINICA Vol. 32, No. 2, 2012, Page 173-182