How does high pressure create layered textures in mica-rich schist?

In mica-rich schist, the characteristic layered texture—known as schistosity—is created through the parallel alignment of platy mineral grains, such as mica, under conditions of directed pressure and deformation.123

When a rock undergoes metamorphism, it is subjected to a stress field that is often not uniform in all directions. As the rock crystallizes or recrystallizes, these directed stresses force the constituent minerals to grow or rotate into a preferred orientation. Because mica minerals are naturally platy or sheety, they align themselves along planes perpendicular to the direction of maximum compressive stress.143

This repetitive, pronounced foliation allows the rock to split easily along these well-defined planes. While schistosity reflects the intensity of metamorphic changes, including high temperatures and pressures, the specific parallel arrangement is a direct response to the rock's structural deformation during its formation.1432