THE RELATIONSHIP BETWEEN Cu CONTENT AND DISTORTION IN THE ATOMIC STRUCTURE OF MELANTERITE FROM THE RICHMOND MINE, IRON MOUNTAIN, CALIFORNIA

The crystal structure of four synthetic samples of melanterite, (Fe,Cu)SO4 •7H2O, and six natural samples of melanterite and one of zinc-melanterite from the Richmond mine, Iron Mountain, California, has been refined in space group P21/c. The structure refinements show that substitution of Cu for Fe at the M2 site distorts the octahedron in a square-planar fashion. This behavior is attributed to the Jahn–Teller distortion induced by incorporation of Cu2+ (d 9 ) at the M2 site. The M1 octahedron does not undergo a similar distortion. Chemical analyses for Fe, Cu and Zn by electron microprobe, AA and ICP–MS reveal a wide variation in the chemical composition of melanterite from this locality, but no strong correlation was found between the proportions of Cu, Fe and Zn and the wide range of colors exhibited by the material. Melanterite with a deep blue color could easily be confused with chalcanthite during field observations.