The mineral commonly used in eyeshadow for shimmer is mica. Mica is a group of silicate minerals whose crystals split into extremely thin, flexible plates that reflect and scatter light.
Cosmetic mica is finely milled and can be used to create luminous, pearlescent, or frosted effects in eyeshadow and other makeup. Its layered crystal structure gives the powder a reflective quality, while pigments or surface treatments provide colors such as gold, bronze, pink, or blue.
Mica is not the same as talc, silica, or zinc oxide, although those materials may also appear in cosmetic formulas for different purposes. Talc can provide slip and absorbency, silica can improve texture or reduce oiliness, and zinc oxide is primarily valued as a white pigment and UV-filtering ingredient in certain products.
The name mica comes from the Latin word mica, meaning “crumb,” probably influenced by micare, “to glitter.” Beyond cosmetics, mica is used in paints, drywall, roofing materials, electronics, and other industrial products because its thin sheets have useful insulating and physical properties.