The coordination environment around Ni at minor concetration levels (2 wt. % NiO) in Na2Si2O5 glass and melt (293--1250 K) has been investigated by Ni K-edge X-ray Absorption Fine Structure (XAFS) spectroscopy. X-ray Absorption Near Edge Structure (XANES) spectra indicate that both IVNi and VNi occur in the glass, whereas IVNi is dominant in the melt. The average anharmonic Ni-O distances derived from XAFS spectra of the glass at 293 K and the melt above 1150 K are 2.00 (¿0.02) and 1.97 (¿0.02) ¿, respectively. The Ni-O distance in the glass is consistent with a mixture of IVNi and VNi, whereas that in the melt is consistent with dominantly IVNi, suggesting a Ni-coordination change during glass melting. This major change in Ni coordination indicates significant reorganization of the melt during quenching and crystallization. These observations for a compositionally-simple melt/glass system may help explain the enrichment of Ni in early-formed igneous minerals. They also suggest the possibility of a pressure-induced coordination change around Ni in the mantle which may influence geochemical modeling of the deep Earth. ¿ American Geophysical Union 1994