Optical absorption spectra of clay minerals

Abst rac t-A preliminary survey of electronic absorption spectra of clay minerals reveals the utility of u.v.-visible spectroscopy in the elucidation of structural, physical, and chemical properties of such systems. Spectra, which were obtained in the suspension, film, and single crystal states (where applic-able), are interpreted in terms of iron-associated transitions. Microcrystalline clay minerals typically show Fe(ll l) in octahedral oxo-ligand geometry whereas mica-type minerals may show a range of iron species, including octahedral Fe(III), tetrahedral Fe(IlI), and octahedral Fe(I1). Iron affects the local site geometry and in "high iron " minerals may dictate layer geometry and subsequently the crystalline form