Mica is an inorganic material found in a wide variety of cosmetic and personal care products. Its use has been reported in more than 7,100 products,1 making it one of the most important mineral ingredients used in cosmetics. Mica is associated primarily with the formulation of color cosmetics, as it is a critical component of hundreds of metal oxide-based inorganic pigments that provide a diverse palette of colors and optical effects.2, 3 Its utility as an optical modifier and tactile modifier have also led to its incorporation in a wide variety of skin and hair care products.2
Chemistry and Manufacture
The term mica refers broadly to a group of closely related hydrous aluminum silicate materials of varying chemical composition; Table 1 lists the chemical formulas of some of the most common types of mica.4, 5 Although mica is a naturally occurring mineral, it should be noted that synthetic micas have been produced and are utilized in cosmetics.6 According to INCI convention, the name Mica only applies to the naturally occurring mineral, and man-made micas are designated as synthetic minerals, e.g., Synthetic Fluorphlogopite. The present article will focus on naturally occurring micas that conform to the INCI definition for mica. The general chemical formula for most micas is W(X, Y)2–3Z4O10(OH, F)2. For the most common mica types, W is typically potassium (K+), sodium (Na+) or calcium (Ca+); the X, Y site is occupied by any two ions of aluminum (Al3+), magnesium (Mg2+), iron (Fe2+, 3+), or lithium (Li+); Z is mainly silicon (Si4+) or Al3+; and the hydroxide (OH-) ions may be partially or completely replaced by fluoride (F-) ions. The most commonly occurring and commercially important types of mica are muscovite and phlogopite; mica-based cosmetic ingredients rely primarily on the muscovite form.