The physico-chemical environment around the aluminum impurity atoms
in commercial Herasil silica is studied by electron-induced X-ray emission
spectroscopy. Despite the low concentration of aluminum and the charging
effect occurring upon electron irradiation, we have been able to characterize
the environment of the Al atoms. We show that the Al atoms are in an
octahedral environment, i.e. surrounded by 6 oxygen atoms. The presence
of Al clusters, whose metallic character would make them candidates to be
ultraviolet absorption centers, is ruled out.