schist, a metamorphic rock with a distinct planar aspect due chiefly to the parallel alignment of some of its constituent minerals, best shown by mica and amphibole (see geology). It has developed a coarser grain-size than slate, having been subjected to greater burial temperatures and pressures, and as a result splits less cleanly. The transition between slate and schist is therefore gradual, and the distinction rather subjective. The rocks of priorat, for example, are described by some as slate and by others as schist. (To add to the confusion, the German word Schiefer is commonly used for both rocks, as is the French word schiste, which is also sometimes extended to include shale.)
