Skeletal morphologies and crystallographic orientations of olivine, diopside and plagioclase

The morphologies and crystallographic orientations of quench-textured olivine, diopside and plagioclase, artificially crystallized at cooling rates of 3-5 °C min−1, have been investigated by scanning electron microscopy (SEM) and Electron backscattered diffraction (EBSD). Olivine displays skeletal, rod-like and dendrite forms with few branches, whereas diopside dendrites have many branches. Plagioclase forms spherulites or euhedral tablets with a porous texture. The skeletal microstructure of these crystals is nearly the same: it consists of H-shaped and dove-shaped units, as described by Donaldson [7] and Faure et al. [5], [6], respectively. When the composition of the starting material lies near the cotectic in the phase diagram, an intergrowth of dendritic diopside and euhedral tablets of plagioclase is formed, and the diopside has a fractal structure. EBSD shows that the skeletal rods of olivine are elongated along 〈0 1 1〉, whereas the branches of the dendritic diopside are elongated along 〈0 0 1〉. These elongation directions are related to the shortest cell parameters in their crystal structures.