[S-MP47_1AM2] Physics and Chemistry of Minerals

[SMP47-12] Structure refinement of legrandite and paradamite : crystal chemistry and hydrogen bonds

*Satoshi JINNOUCHI¹, Akira YOSHIASA¹, Kazumasa SUGIYAMA², Hiroshi ARIMA², Reiko SHIMURA², Riturou MIYAWAKI³ (1.Graduate School of Science and Technology, Kumamoto University., 2.Institute for Materials Research, Tohoku University, 3.National Science Museum)

Keywords:structure refinement, legrandite, paradamite, crystal chemistry, hydrogen bonds

Legrandite, Zn₂AsO₄(OH)H₂O and paradamite, Zn₂AsO₄(OH), are zinc arsenate minerals and have a color between pale yellow and yellowish brown. Related minerals of legrandite and paradamite are adamite, Zn₂AsO₄(OH), and so on with different structures. We performed the structure refinement of legrandite and paradamite Oujela Mine, Mapimi, Durango, Mexico, by (RAPID) RIGAKU single-crystal structure analysis system. We determined the hydrogen position by difference Fourier method. We revealed the detail hydrogen bond using bond valence calculation and hydrogen positions and compared crystal structures of these. The structure of legrandite is constituted by two AsO₄ tetrahedrons, ZnO₆ octahedron and three ZnO₅ trigonal dipyramids that have large unique distortion. AsO₄ tetrahedron, ZnO₅ trigonal dipyramid and ZnO₆ octahedron constitutes the unique framework. The structure of paradamite is constituted by AsO₄ tetrahedron and two ZnO₅ trigonal dipyramid that have large unique distortion. In legrandite, 5 coordination of trigonal dipyrmids have a distance to be expected from ionic radii but interatomic distance of Zn(3)-O(1) has extraordinary distance. Two OH groups bond to Zn1 and Zn2, Zn3 and Zn4 make the ZnO₃(H₂O)₂ trigonal dipyramid that is bonded to two H₂O group in legrandite. In paradamite, Zn1 and Zn2 make ZnO₃(OH)₂ and ZnO₄(OH) trigonal dipyramid. Hydrogen atoms make a lot of hydrogen bonding in legrandite and paradamite. Crystal structure of legrandite has a tunnel structure continuous that is only parallel to c axis and similar structure is observed in paradamite only parallel to a axis. There are path of proton-conduction in these direction and we conjecture that these proton-conductivity have large anisotropy of one dimension.