Mass transfer in sillimanite-bearing pelitic schists near Rangeley, Maine Available to Purchase

Reactions in pelites from the lower sillimanite zone on Elephant Mountain in the Rangeley-Oquossoc region are of the cation-exchange type involving diffusion among three assemblages in local equilibrium. Sillimanite nucleated preferentially in biotites near garnets and formed segregations containing sillimanite-rich cores and biotite-rich mantles. Chemical potential gradients between the growing sillimanite, the preexisting staurolite, and matrix garnets caused mass transfer which led to the pseudomorphing of staurolite by micas and the growth of garnet at the expense of matrix. Mass transfer between the sillimanite, staurolite, and garnet segregations has been measured and is compatible with a cation-exchange reaction mechanism in a system open to water. The component with the largest mass transfer in a mean molar reference frame is AlO_1.5 followed in descending order by SiO₂, H₂O, KO_0.5, FeO, NaO_0.5, MgO, MnO, TiO₂ and CaO.