A reddish mineral now regarded as a variety of biotite.

A variety of biotite, n., in which iron replaces much of the magnesium.

(a) a hydrated variety of biotite; (b) any clay composed of an intimate mixture of biotite and vermiculite.

a dark green to black iron-rich mineral of the mica group occurring typically in pegmatites.

A micaceous aluminosilicate of manganese of a copper-red colour, probably an altered form of biotite.