Paratacamite-(Ni), Cu3(Ni,Cu)Cl2(OH)6, a new mineral from the Carr Boyd Rocks mine, Western Australia

Paratacamite-(Ni)(IMA 2013-013), Cu3(Ni,Cu)Cl2(OH)6, is a new Ni-rich mineral with the paratacamite structure. It occurs in the Carr Boyd Rocks nickel mine, Western Australia, as a supergene alteration phase in association with gillardite, spaugolite and gypsum. Paratacamite-(Ni)occurs as aggregates of equant rhombohedral crystals up to ca2 mm in size and exhibits the forms {101}, {021} and {001}. The mineral is dark green with a light-green streak, transparent and has a vitreous lustre. It has good cleavage on {1011}. Measured and calculated densities are 3.70 and 3.735 g cm-3, respectively. Optically, paratacamite-(Ni) is uniaxial (-) with ѡ and E > 1.8. The average of eight electron-microprobe analyses gave the empirical formula Cu3(Ni0.71 Cu0.27 Co0.02)Cl2(0H)6. The new mineral is trigonal, space group R3, with a=13.682(2) and c=13.916(2) Å,V=2256.0(7) Å3 and Z=12. The strongest reflections in the X-ray powder diffraction pattern are [dobs Å(1)(hkl)]: 5.445(81)(021),4.637(13)(003), 4.505(8)(202),2.894(21)(401),2.751(100)(223), 2.254(65)(404), 1.815(14) (603) and 1.708(9)(440). The structure refined to R1 = 0.0225 and ѡR2 = 0.0660 for 314 reflections with Fobs> 4σ(Fobs). The (2+2+2) Jahn-Teller distortion present in the M(2)O6 octahedron suggests that the new mineral is close to the limit of Cu2+ substitution by Ni2+.