Namely
Mica is a mineral often used as a white dye in make-up products, it can also be used as an opacifier. It is also represented in the INCI list by its ColorIndex, CI 77019.
Its functions (INCI)
Anticaking : Helps ensure the fluidity of solid particles and limit their agglomeration in powder cosmetic products or hard mass cosmetics.
Bulking : Reduces apparent cosmetics density.
Cosmetic colorant : Color cosmetics and / or give a color to the skin
Opacifying : Reduces transparency or translucency of cosmetics