Structural Analysis of Chrysocolla by Anomalous X-ray Scattering (AXS) Coupled with Reverse Monte Carlo (RMC) Simulation

Department of Earth and Planetary Science, The University of Tokyo* Department of Radiological Technology, School of Health Sciences, Niigata University, Japan**
â—‹Yasutaka Takemaru* Kazumasa Sugiyama* Masatoshi Saito**

Chrysocolla is found in the oxidized zone of copper deposits associated with malachite, azurite, cuprite, or native copper. Chrysocolla was believed to be the mixture of crystalline Cu and Cu oxide, as well as amorphous silica [1]. The main purpose of this study is to provide the quantitative structural information of such chrysocolla by using the anomalous X-ray scattering (AXS) measurement coupled with reverse Monte Carlo (RMC) simulation.
The X-ray scattering profiles of a chrysocolla sample ((CuO)0.5(SiO2)0.6(H2O)1.1; Dm=2.2Mg/m3) were measured at the Cu K-absorption edge and the observed energy dependence in scattering intensities was employed in order to obtain the environmental radial distribution function (RDF) around Cu. The ordinary RDF analysis was also carried out by using Mo Ka radiation. The obtained RDFs clearly suggest that the correlation distances of the nearest neighbor Si-O and Cu-O are around 0.16nm and 0.20nm, respectively. These distances are similar to those of SiO4 and CuO4 in dioptase (Cu6Si6O18 6H2O), and the structural information around Cu is consistent with that obtained by XAFS study, in particular [2]. However, the RMC simulation indicates that the average coordination numbers of the nearest oxygen around Si and Cu were approximately three and four, respectively. These results could be explained by introducing the unusual SiO3 coordination found in Si10O15H10, only.
[1] F.V.Chukhrov, B.B.Zvyagin, A.I.Gorshkov, L.P.Ermilova & E.S.Rudnitskaya, Izvest. Akad. Nauk SSSR, Ser. Geol., 6(l968)29.
[2]D.A.McKeown: J. Non-Crystalline Solids, 180(1994)1.