Cobalt-bearing adamite from Cap Garonne, Mine du Pradet, France - structural relationship to olivenite and magnetic behavior

The crystal structure of cobalt-bearing adamite (Zn, Co)(2)AsO4OH (so-called cobalton adamite) from Mine du Pradet, Cap Garonne, France has been refined from single crystal X-ray diffraction data: Pnnm, a = 831.39(4), b = 852.67(6), c = 605.84(6) pm, wR = 0.0568, 901 F-2 values, 48 variables. The composition of the single crystal and the bulk sample with EDX and ICP-OES was determined as Zn1.94Co0.06(AsO4)OH and (Co0.085Ni0.037Cu0.270Zn1.608)AsO4OH. The Co2+, Ni2+ and Cu2+ incorporation in the bulk sample leads to Curie paramagnetism with an experimental moment of 2.85 mu B/M2+ cation and explains the pink color along with the greenish edges. The Raman spectrum shows the characteristic vibrations of the AsO4 tetrahedra and the MO5 pyramids as well as the O-H stretching mode. The adamite structure is closely related with the olivenite type (space group P2(1)/n11). This structural relationship is discussed on the basis of a group-subgroup scheme (B & auml;rnighausen formalism).