Diffuse Reflectance Spectra and Optical Properties of Some Iron and Titanium Oxides and Oxyhydroxides

R. G. J. Strens1 and B. J. Wood
School of Physics, The University, Newcastle upon Tyne NE1 7RU
Department of Geology, The University, Manchester M13 9PL
1Present address: Department of Mineralogy and Petrology, Downing Place, Cambridge CB2 3EW.

Summary: The reliability and utility of diffuse reflectance spectra are briefly but critically reviewed. The results of measurements of diffuse reflectance over the wavelength range 200 < γ < 2500 nm are reported for wüstite, magnetite, hematite, maghemite, ilmenite, ulvöspinel, and α-FeO · OH (goethite), β-FeO 7sd OH, γ-FeO · OH (lepidocrocite), and δ-FeO · OH. The spectra have been assigned by reference to simplified molecular-orbital energy-level diagrams derived from recent SCF-Xα calculations.

The specular reflectances reported in the Quantitative Data File (Henry, 1977) are related to the diffuse reflectance spectra in a rational way. Minerals that absorb strongly throughout the visible display little dispersion of specular reflectance, and their powders are dark (wüstite, magnetite, ilmenite, ulvöspinel); those that absorb much more strongly in the near ultraviolet than in the visible have specular reflectances that decrease monotonically from blue to red according to a simple dispersion relation derived by combining the Sellmeier dispersion and Fresnel reflexion equations; their powders are strongly coloured (hematite, maghemite, lepidocrocite, goethite) and their optical anisotropy is closely related to crystal structure.

Mineralogical Magazine; September 1979 v. 43; no. 327; p. 347-354; DOI: 10.1180/minmag.1979.043.327.06
© 1979, The Mineralogical Society
Mineralogical Society (www.minersoc.org)