Poster - Microstructures of Metamorphic Rocks Microstructures of Metamorphic Rocks Analysing crystal size distributions Since the nucleation rate is so sensitive to overstepping, the shape of the crystal size distribution is dominated by the changes in nucleation rate with time. In most examples, the right-hand tail of the distribution, reflecting the initial acceleration of the nucleation rate, looks like an exponential function. These factors determine the initial acceleration of nucleation rate, measured by the parameter b.
Large b corresponds to many small crystals, and small b to scattered large porphyroblasts.
Here are plots for the other two examples, showing variation in the value of b for different minerals in different settings.