Fast crystal-growth rates can lead to the disequilibrium partition of trace and major elements in igneous rocks and to modification of the compositional path taken by an intrusive, fractionating magma. Kinetic variations in partition coefficients may be used to determine crystal-growth rates in selected cases, by the Burton, Prim and Slichter theoretical model (1953). Fission track analysis has been used to study the variation in uranium concentration in olivines of different morphologies from the Rhum layered intrusion, Scotland, and the BPS model used to assess the average crystal growth rate for each morphological type. The growth rate for the harrisitic morphology was approximately five times faster than that for the equant morphology. Reliable data, especially on diffusion coefficients of appropriate elements, are needed before absolute growth rates may be calculated.