Muscovite is abundant in low to medium grade metamorphic rocks, especially meta-pelites, and is common in granitic rocks.  It is typically colourless in plane polarized light and has moderate positive relief relative to quartz and feldspars and, like talc, shows changes in relief with rotation of the stage.  It usually occurs as flakes with well-developed pinacoid {001} surfaces parallel to the perfect basal cleavage (A).  Maximum interference colours range to third order and extinction is parallel to cleavage and pinacoid surfaces (B).  Muscovite has a mottled or “crinkly” appearance at or near extinction (B), as do many other phyllosilicates.  In C, coarse, colourless grains of muscovite occur in feldspars that are cloudy in plane light due to alteration (sericite), also seen in D, where the coarse and fine micas show second order interference colours.  A and C ppl, B and D x-nicols.  A and B are from a two-mica garnet schist  and C and D are from a granite, both from unknown locations. Views A and B are 2.2 mm across, C and D are 5.5 mm across.  A and C ppl, B and D x-nicols.