Aluminum K-edge XANES spectra of high pressure and high temperature (4.4 GPa and 1575 ¿C) glasses along the NaAlSi2O6(Jd)-NaAlSi3O8(Ab) join are reported using synchrotron radiation, and shown to provide direct experimental evidence for the pressure-induced coordination change of Al. Five- and six-fold coordinated Al ([5>Al and [6>Al), characterized by Al K-edge positions at 1567.8 and 1568.7 eV, respectively, first appear in glass of composition Jd60Ab40 and increase in proportion progressively with increasing Jd content. The end-member jadeite glass contains about 6% of each of [5>Al and [6>Al. The present direct measurements confirm literature suggestions for the important role of Al in controlling viscosity and diffusion in mantle melts. ¿ American Geophysical Union 1995