The indentification of iron in the M(4) site of calcic amphiboles
Don S. Goldman and George R.
Rossman
Division of Geological and Planetary
Sciences
California Institute of Technology
Pasadena, CA 91125
Abstract
Evidence is presented for the occurrence
of Fe2+
in the predominantly Ca-filled M(4) site of calcic amphiboles.
Absorption bands in the electronics pectra at 1030 nm in beta and at
2470 in alpha provide a sensitive means for identifying Fe2+
in this site.The large epsilon value for the 1030 band, the large
energy separation between both bands, and the similarity to the spectra
of Fe2+ in large, highly distorted coordination sites in
other minerals provide the basis for the M(4) site assignment. The
energy splittings and polarization anisotropy of these bands are
analyzed, using a point-charge model based on C2v symmetry.
Spectral data indicate that the Fe2+ content in the M(4)
site varies significantly amongt he calcic amphiboles.
Room temperature spectrum of Fe2+
in tremolite from Mt. Bity
