Agardite-(Y), Cu(2+) (6)Y(AsO(4))(3)(OH)(6)·3H(2)O

Agardite-(Y), with a refined formula of Cu(2+) (5.70)(Y(0.69)Ca(0.31))[(As(0.83)P(0.17))O(4)](3)(OH)(6)·3H(2)O [ideally Cu(2+) (6)Y(AsO(4))(3)(OH)(6)·3H(2)O, hexa­copper(II) yttrium tris­(arsenate) hexa­hydroxide trihydrate], belongs to the mixite mineral group which is characterized by the general formula Cu(2+) (6) A(TO(4))(3)(OH)(6)·3H(2)O, where nine-coordinated cations in the A-site include rare earth elements along with Al, Ca, Pb, or Bi, and the T-site contains P or As. This study presents the first structure determination of agardite-(Y). It is based on the single-crystal X-ray diffraction of a natural sample from Jote West mine, Pampa Larga Mining District, Copiapo, Chile. The general structural feature of agardite-(Y) is characterized by infinite chains of edge-sharing CuO(5) square pyramids (site symmetry 1) extending down the c axis, connected in the ab plane by edge-sharing YO(9) polyhedra (site symmetry -6..) and corner-sharing AsO(4) tetra­hedra (site symmetry m..). Hy­droxyl groups occupy each corner of the CuO(5)-square pyramids not shared by a neighboring As or Y atom. Each YO(9) polyhedron is surrounded by three tubular channels. The walls of the channels, parallel to the c axis, are six-membered hexa­gonal rings comprised of CuO(5) and AsO(4) polyhedra in a 2:1 ratio, and contain free mol­ecules of lattice water.