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  • Fe2+/Fe3+ Intervalence Charge Transfer and Enhanced d - d Absorption in Mixed Valence Iron Minerals at Elevated Temperatures

This content will become publicly available on July 2, 2026

Title: Fe2+/Fe3+ Intervalence Charge Transfer and Enhanced d - d Absorption in Mixed Valence Iron Minerals at Elevated Temperatures
Abstract The absorption of light by Fe/Ti and Fe/Fe intervalence charge transfer (IVCT) bands has previously been found in aluminum oxide and Al2SiO5 aluminosilicate minerals to decrease markedly at elevated temperatures. Given the abundance of iron at depth in the Earth, assessing the generality with which and extent to which IVCT mineral phases become more optically transparent at temperature than they are under ambient conditions has potentially significant implications for the modeling of mantle geophysical processes such as radiative conductivity. A broad experimental survey of the optical absorption spectra at elevated temperatures of various mixed valence iron minerals has been conducted. The minerals considered here are cordierite, chloritoid, lazulite, dumortierite, jeremejevite, beryl, osumilite, biotite (mica), pargasite (amphibole) and aegirine (pyroxene). All samples transiently lose significant Fe/Fe IVCT feature intensity at temperature. In beryl, osumilite, biotite, pargasite and aegirine, spin-allowed Fe2+d-d features also decrease in integral intensity at temperature; in all but beryl, the intensity loss is significant. This trend is consistent with d-d band enhancement via Fe2+/Fe3+ exchange coupling, which has not previously been identified in the majority of these minerals. It is contrasted against the behavior of ordinary spinallowed Fe2+d-d bands in non-IVCT minerals forsterite (olivine) and elbaite (tourmaline). The depletion of Fe/Fe IVCT and enhanced Fe2+d-d band intensity at elevated temperatures may both be important mechanisms by which iron-bearing mineral phases become more optically transparent under conditions at depth.  more » « less
Award ID(s):
2148727
PAR ID:
10659904
Author(s) / Creator(s):
;
Editor(s):
Tomascak, P; Nestola, F
Publisher / Repository:
American Mineralogist
Date Published:
Journal Name:
American Mineralogist
ISSN:
0003-004X
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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