Mika generate from clay mineral re-crystallization. It’s always to produce in the process of metamorphism in Shale and mudstone. So we can always see the shining on the back phyllite and schist in the sun. The reflective effect comes from mica. Slate and sandstone also contains mica but the crystallinity is poor so the reflective effect is not obvious. The characteristics 0f mica will with higher dielectric strength and lager resistance and high temperature resistance. So it is use in cosmetic for smooth skin and adhesion.