Mineral segregation can occur during aging of crystal assemblages as areas composed of nominally larger grains grow at the expense of nearby, smaller grains owing to solution concentration variations that arise from surface energy effects. The "competitive particle growth' model of Ortoleva and co-workers has been extended to consider aging of two crystal phases in a two-component liquid and to include the heat of crystallization. Numerical modelling demonstrates that if the liquid buffering ability of both minerals "a' and "b' are similar, the system will evolve to areas composed of a and b surrounded by regions where both minerals have dissolved completely; there is otherwise no segregation of a and b. However, when the reaction of mineral "b' to changes in solution concentration is slow relative to mineral "a', a patterned segregation of minerals can occur. The pattern sequence is then (a + b) - b - (a + b)..., a sequence common in many examples of fine-scale layering. -from Author