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

Abstract

Abstract The crystal structure of cobalt-bearing adamite (Zn, Co)2AsO4OH (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 µB/M 2+ 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 P21/n11). This structural relationship is discussed on the basis of a group–subgroup scheme (Bärnighausen formalism).