COORDINATION CHANGE AROUND 2WT-PERCENT NI IN NA2SI2O5 GLASS MELT SYSTEMS

The coordination environment around Ni at minor concentration levels ( 2 wt% NiO) in Na2Si2O5 glass and melt has been investigated by high te mperature (293-1250 K) X-ray absorption fine structure (XAFS) spectros copy. The derived average anharmonic Ni-O distances for the glass at 2 93 K and the melt above 1150 K are 1.99 (1) and 1.97 (1)Angstrom, resp ectively. The Ni-O distance in the glass is consistent with a mixture of Ni-IV and Ni-V, whereas that in the melt is consistent with dominan tly Ni-IV. The significant reorganization of the melt during quenching may help explain the enrichment of Ni in, early-formed igneous minera ls. These data also suggest the possibility of a pressure-induced coor dination change around Ni, which may influence significantly the geoch emical modeling of the Earth.