Phlogopite

Phlogopite is a yellow, greenish, reddish-brown member of the mica family of phyllosilicates. It also known as magnesium mica.

Phlogopite is the magnesium endmember of the biotite solid solution series. Iron substitutes for magnesium in variable amounts leading to the more common biotite with higher iron content. For physical and optical identification, it shares most of the characteristic properties of biotite.

Phlogopite micas found primarily in igneous rocks, although it is also common in contact metamorphic aureoles of intrusive igneous rocks with magnesian country rocks and in marble formed from impure dolomite (dolomite with some siliclastic sediment).