Abstract

Iron-57 Mossbauer spectra and polarized absorption spectra in the region of 4000-6800 Angstroms are reported for 14 common pegmatitic muscovites, 12 of which were selected from an extensive pegmatite complex. They were chosen to cover a wide range of colour types (deep green, green, red-green and ruby-red) and ferric/ferrous ion ratios. Optical absorption properties are discussed in terms of the Fe (super 2+) , Fe (super 3+) distribution in the M1 and M2 sites. Background absorption, and hence depth of color, appears to be determined primarily by an intense metal-ligand charge transfer which peaks in the UV and the intensity of which correlates linearly with the Fe (super 2+) concentration in the normally unoccupied M2 site. The presence or absence of the Fe (super 2+ or -Fe (super 3+) metal-metal charge transfer bands in the region of 5000-6000 Angstroms give rise to the red and green hues observed in the muscovites studied

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