mineral makeup is free of preservatives, chemicals, fillers, fragrance. etc.
Bare Escentuals was, i think, one of the first mineral makeup companies on the market. They seem to have done very well which could explain why more drugstore brands might want to venture out to mineral makeup.
I use this Physicians Formula powder and I love it. The coverage isn't that great since it's sheer but it does a nice job of evening out my skin tone. It doesn't make me break out a single bit either.