Don S. Goldman

Determination of quantitative cation distribution in orthopyroxenes from electronic absorption spectra

Electronic and Mössbauer absorption spectra and electron microprobe data are correlated for iron-bearing orthopyroxenes. The correlation provides a means of quantitatively determining the distribution of Fe2+ between the M(1) and M(2) sites of orthopyroxene crystals from electronic spectra and electron microprobe analysis. The electronic spectra are used to analyze the changes in the Fe2+ distribution produced during heating experiments and confirm earlier results from Mössbauer spectra. Two components of the spin-allowed transition of Fe2+ in the M(1) site are identified at about 13,000 cm−1 and 8,500 cm−1 in γ. Molar absorptivity (ɛ) values for all spin-allowed Fe2+ absorption bands in the near-infrared region are determined. The M(2) Fe2+ band at ∼5,000 cm−1 in β is the analytically most useful for site occupancy determinations. It remains linear with concentration (ɛ=9.65) over the entire compositional range. The band at ∼10,500 cm−1 in α is the most sensitive to M(2) Fe2+ concentration (ɛ=40.8), but deviates from linearity at high iron concentrations. The origins of spin-forbidden transitions in the visible region are examined.

Spectral study of ferrous iron in CaAlborosilicate glass at room and melt temperatures

Abstract Ferrous iron absorption in the near-infrared region has been examined in CaAlborosilicate glass at room and melt temperatures. Based upon mineral spectra, ferrous iron is concluded to occupy a variety of modifier positions of different sizes in the glass structure. A new emission technique is used to collect spectral data of molten glass. Absorption at room temperature and 1260 °C is similar and no difference could be detected at different melt temperatures, once oxidation effects are eliminated. Oxidation and dehydroxylation occur simultaneously at melt temperatures, but these processes are probably not mutually dependent.

Identification of a mid-infrared electronic absorption band of Fe2+ in the distorted M(2) site of Orthopyroxene, (Mg, Fe)SiO3

An electronic absorption band of Fe^(2+) in the distorted, six-coordinate M(2) site of the common mineral orthopyroxene, (Mg, Fe)SiO_3, is identified at 2350 cm^(−1). This band is attributed to the A_1 → B_2 transition within the split ^5T_(2g) state of Fe^(2+) in C_(2V) symmetry.