Complex sentence: Schist is a medium-grade metamorphic rocks with medium to large grains of mica flakes in a preferred orientation, in foliated (composed of sheet-like layerss) arrangement called "schistocity".
Split into simpler sentences: Schist is a medium-grade metamorphic rock with medium to large grains of mica flakes in a preferred orientation. Geological foliation (metamorphic arrangement in layers) with medium to large grined mica flakes in a preferred sheetlike orientation is called "schistocity".