micropegmatite

micropegmatite, quartz and alkali feldspar intergrowth so fine that it can be resolved only under the microscope; it is otherwise indistinguishable from the coarser intergrowths known as graphic granite. The quartz-feldspar interfaces are planar, and the quartz areas tend to be triangular in cross section. These patches of quartz are in parallel optical orientation, and it was long supposed that they were actually continuous, either above or below the plane of observation; a detailed study...