This soft white powder is used in cosmetics to improve adhesion and slip, and texture. Generally it is used in concentrations of 5% - 10% by weight in a loose powder.
Magnesium Stearate is a chemical compound of Magnesium (element, same as in vitamins) and Stearate (plant derived). General shelf life is 2 years if kept in a cool, dark, air tight container/location.
Magnesium stearate is used in foundations, face powders, eyeshadows and lipsticks. Additionally, it can also be used in creams, lotions and pomades.