Summary: The local development of strongly oxidizing conditions during crystallization of a recent basalt lava lake on Piton de la Fournaise, Réunion, led to the production of approximately 15 % residual rhyodacite liquid. This was segregated into the vesicle cavities as the lava solidified, and congealed as a glass containing microlites of feldspar, clinopyroxene, and hematite. The rhyodacite is compared chemically with the residual glasses recorded from other basaltic and doleritic occurrences, and with the Mauna Kuwale rhyodacite of Oahu.