mica | Structure, Properties, Occurrence, Facts | Britannica
Sep 13, 2022 · mica, any of a group of hydrous potassium, aluminum silie minerals. It is a type of phyllosilie, exhibiting a twodimensional sheet or layer structure. Among the principal rockforming minerals, micas are found in all three major rock varieties—igneous, sedimentary, and metamorphic. Of the 28 known species of the mica group, only 6 are common rockforming .