We study oscillatory banding in plagioclase and pyroxene crystals from different volcanic environments. We use digitized images from an optical microscope. Assuming that oscillatory banding is selfaffine, we calculate the Hurst coefficient H, for each crystal, used here as a phenomenological characterization of banding. We find that calculated values of H are reproducible, not only in crystals from the same thin section, but also in rocks from the same environment. Plagioclase crystals from different volcanoes exhibit different values of the Hurst coefficient H.