Fe²⁺ - Ti⁴⁺ Charge Transfer in Stoichiometric Fe²⁺, Ti⁴⁺-Minerals

Optical absorption spectra are presented for taramellite, traskite and neptunite, allof which have both Fe²⁺ and Ti⁴⁺ 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 8000 cm^-1 half-width. These transitions, assigned to Fe²⁺-Ti⁴⁺ intervalance charge transfer, showed litted difference in intensity at 80 and 300 K and have molar absorptivities which range from ~100 to ~1300 M^-1cm^-1. The Fe²⁺-Ti⁴⁺ absorptions in these standards generally compre well to other mineral spectra in which Fe²⁺-Ti⁴⁺ intervalence absorption has previously been proposed with the exception of the most cited example, blue corundum.