Both muscovite and biotite are present in the plane-polarized view below. The muscovite is barely visible.
In crossed polarizers, muscovite generally has vivid second- and third-order colors. The interference colors of biotite are a bit lower order and more subdues because of biotite's coloration. Note the relative lack of mottling in the muscovite compared to the biotite.
Where there are no dark minerals, muscovite in plane-polarized light is nearly invisible. It shows up only by its slightly higher relief than quartz and feldspar.
The same field in crossed polarizers. The bright outlines are thin edges where the muscovite shows only first-order white colors because of its thinness.
Below are two more fairly typical crossed-polarizer views of muscovite.
Created 22 Sept 1997, Last Update 16 December 1999
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