Single-crystal Mossbauer studies, supplemented by polarized optical- absorption measurements, were used to determine the EFG alignments of Fe (super 2+) in the M1 and M2 sites and Fe (super 3+) in the M1 site of three muscovites of varying Fe composition and colour type. The EFG alignments differ markedly in the three crystals. In conformity with the requirements of crystal symmetry, but contrary to earlier reported results, the EFG symmetries are distinctly rhombic: n = 0.68, 0.70, and 0.93 for Fe (super 2+) over M1 , Fe (super 2+) over sub M2/, and Fe (super 3+) over M1/, respectively. There is a strong tendency for either V yy or V zz to align along an M1-M2 (or M1-M1) direction, particularly in a high Fe (super 2+) (red-coloured) muscovite.

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