Dyar, M. D. — Page 3 | Engineering Papers

NASA NTRS1983

Spectral chemistry of green glass-bearing 15426 regolith

The detection of appreciable concentrations of ferric iron in a synthetic green glass equilibrated at an oxygen fugacity of 10 to the -11th atm prompted a Moessbauer spectral study of pristine emerald-green glass spherules carefully handpicked from regolith sample 15426. No Fe(3+) ions were detected in this lunar sample or in a synthetic green glass simulant equilibrated at fO2 = 10 to the -14th atm, suggesting that the green glass clods in rock 15426 formed under conditions of correspondingly low oxygen fugacities. The Moessbauer spectra indicated the presence of olivine crystallites in the lunar emerald green glass spherules. Measurements of homogeneous and partially devitrified synthetic silicate glasses revealed that significant changes of coordination environment about Fe(2+) ions in the glass structure occur during crystallization of olivine crystals from the melt.

Burns, R. G.↗

NASA NTRS1982

Coordination chemistry of iron in glasses contributing to remote-sensed spectra of the moon

Ferric iron and tetrahedrally coordinated Fe(2+) ions are identified using Moessbauer and electronic absorption spectroscopic measurements of synthetic glasses equilibrated at P(O2) less than 10 to the -11 atm, simulating the Luna 24 brown glass and Apollo 15 green glass compositions. The presence of 10-20% ferric iron in these low Ti glasses is a result of the absence of Ti(3+) ions. In the brown glass absorption spectra, tetrahedral Fe(3+) and Fe(2+) ions induce an extension of the oxygen-metal charge transfer band into the visible region further than in the green glass containing predominantly octahedral Fe(2+) and Fe(3+) ions. Whereas the glass one-micron band originates from crystal field transitions in octahedral Fe(2+), the glass two-micron band is now positively correlated with tetrahedral Fe(2+) rather than with Fe(2+) ions in pyroxene M2-like sites in the glass structure. The tetrahedral Fe(2+) do not, however, substitute for Si(4+) in glass network-forming sites, instead occurring as network modifiers in larger tetrahedral interstices. The effect of temperature is to induce a pronounced red-shift of the oxygen-iron charge transfer absorption edge, especially for the brown glass, and to intensify significantly the tetrahedral Fe(2+) crystal field two micron band.

Dyar, M. D.↗