How are minerals biotite mica and muscovite mica different?

Biotite mica contains iron and/or magnesium, but muscovite mica does not.

Muscovite is but one of a number of micaceous minerals.

Mica meets all of the requirements of a mineral; solid, naturally occurring, crystalline structure, specific range of chemical formulae, and inorganic.

Biotite mica is dark, muscovite mica is light in color.

Mica is a group of minerals, yes.