Zoning predicted for garnet/biotite Fe exchange reactions. In this experiment both grain boundary and lattice concentrations are shown with the same look up table, (but with different scaling). The grain boundary concentrations show the gradual loss of Fe from the Biotite, and the lattice concentrations show the preferential enrichment at garnet grain boundaries, but also the preferential enrichment around the perimeter of the cluster, and finally the preferential enrichment where the biotite grains are nearest. Zoning patterns are roughly concentric with respect to current grain boundaries. Note that this model has cyclic limits, so that the biotite grains are also ?near? below and to the right of the cluster. Figure 1 Starting model configuration. Garnet grains are red, biotite grains are yellow, matrix grains are green, grain boundaries are white, and blue dots show the location of unconnected nodes that store lattice chemistry information. Mark Jessell