Figure 51 (a) Muscovite, showing its strong basal cleavage (smaller flake is 3 cm across). (b) Plane-polarised light image of muscovite in a garnet mica schist. The muscovite is colourless. Obvious cleavage traces run along the length of the grain, but because the rock is deformed, they have a bent or wavy appearance (field of view 7.5 mm across). (c) The same field of view as in (b) between crossed polars; muscovite has bright second- to third-order interference colours.