Basaltic glass inclusions trapped in plagioclase phenocrysts (An84) are
remnant of their parent magmatic liquid. They can be used as natural
reactors for the experimental investigation of olivine growth rate as a
function of temperature. The growth of one olivine nucleus can be
observed at constant temperature. Supercooling from 15-degrees to
150-degrees-C have been investigated. Growth habits vary from equant to
feather in qualitative agreement with previous studies. Growth rates
vary from < 10(-10) m s-1 to 6.10(-7) m s-1; they vary with the
direction, the growth process (planar or dendritic) and the degree of
supercooling. Chemical analysis of crystal overgrowth and the remaining
liquid composition enables a mass-balance calculation which confirms the
rates determined optically. The small number of results obtained so far
does not permit to draw inferences on the growth mechanisms.