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


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.

Mt Bity Tremolite      
Room temperature spectrum of Fe2+ in tremolite from Mt. Bity

last updated: 23-Jul-2023