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) 2 AsO 4 OH (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, w R = 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 Zn 1.94 Co 0.06 (AsO 4 )OH and (Co 0.085 Ni 0.037 Cu 0.270 Zn 1.608 )AsO 4 OH. The Co 2+ , Ni 2+ and Cu 2+ incorporation in the bulk sample leads to Curie paramagnetism with an experimental moment of 2.85 µ B / M 2+ cation and explains the pink color along with the greenish edges. The Raman spectrum shows the characteristic vibrations of the AsO 4 tetrahedra and the M O 5 pyramids as well as the O–H stretching mode. The adamite structure is closely related with the olivenite type (space group P 2 1 / n 11). This structural relationship is discussed on the basis of a group–subgroup scheme (Bärnighausen formalism).