Hi! Thanks for your question!
Mineral makeup is inorganic and contains no moisture, therefore bacteria cannot form and thrive, which is why no preservatives are needed to stabilize high-quality mineral products. Furthermore, these products will not spoil because they contain no fillers or synthetic dyes. So in theory, mineral makeup will last forever.
However, it is possible for you to transmit organic material to the makeup if you allow a brush to contact the makeup after the brush has been on your face. Try to avoid dipping used makeup brushes directly into your main container of mineral makeup. A good alternative is to pour some out for application onto a clean, washable surface or into a little bowl.
As a rule of thumb, you should toss any cosmetics when they take on an unattractive change in their color, texture or odor.