Fe^(2+)-Ti^(4+) charge transfer in stoichiometric Fe^(2+),Ti^(4+) -minerals

Abstract

Optical absorption spectra are presented for taramellite, traskite and neptunite, all of which have both Fe^(2+) and Ti^(4+) as major elements. The spectra of each of these minerals are dominated by a single, intense absorption band in the 415 to 460 nm region with 7000 to 9000 cm^(−1) half width. These transitions, assigned to Fe^(2+)-Ti^(4+) intervalence charge transfer, showed little difference in intensity at 80 and 300 K and have molar absorptivities which range from ∼100 to ∼1300 M^(−1) cm^(−1). The Fe^(2+)-Ti^(4+) absorptions in these standards generally compare well to other mineral spectra in which Fe^(2+) — Ti^(4+) intervalence absorption has previously been proposed with the exception of the most cited example, blue corundum.