title: Cation diffusion in plagioclase feldspar.
abstract: Steep compositional gradients in igneous plagioclase feldspar from slowly cooled intrusive bodies imply a maximum value of the intracrystalline diffusion coefficient for NaSi [unknown] CaAl exchange, D(max) approximately 10(-20) centimeters squared per second for temperatures in the range 1250 degrees to 1000 degrees C. Millimeter-sized grains cannot be homogenized in all geologic time; hence reactive equilibrium crystallization of plagioclase from the melt does not occur in dry systems.
authors.forename: S A
authors.initials: SA
authors.lastname: Morse