Structural and compositional variations of basic Cu(II) chlorides in the herbertsmithite and gillardite structure field

摘要

Natural samples of the substituted basic Cu(II) chloride series, Cu4-xMx2+(OH)(6)Cl-2 (M= Zn, Ni, or Mg) were investigated by single-crystal X-ray diffraction in order to elucidate compositional boundaries associated with paratacamite and its congeners. The compositional ranges examined are Cu3.65Zn0.35(OH)(6)Cl2Cu3.36Zn0.64( OH)(6)Cl-2 and Cu3.61Ni0.39(OH)(6)Cl-2 - Cu3.13Ni0.87(OH)(6)Cl-2, along with a single Mg-bearing phase. The majority of samples studied have trigonal symmetry (R (3) over barm) analogous to that of herbertsmithite (Zn) and gillardite (Ni), with a approximate to 6.8, c approximate to 14.0 angstrom. Crystallographic variations for these samples caused by composition are compared with both published and new data for the R (3) over barm sub-cell of paratacamite, paratacamite-(Mg) and paratacamite-(Ni). The observed trends suggest that the composition of end-members associated with the paratacamite congeners depend upon the nature of the substituting cation.