ELECTRON SP IN RESONANCE STUDIES OF HALLOYSITES

ABSTRACT: Absorption lines in the g ~ 4 region of ESR spectra of three New Zealand halloysites were found to originate from similar paramagnetic centres as in kaolinites. Resonances in the g ~ 4 region were not common to all the halloysites, although the signal at g = 2.0 for the Matauri Bay halloysite isprobably due to a trapped positive hole or trapped O5 ion. A 6-line resonance produced by Te Puke halloysite and removable by Na-saturation is attributed to exchangeable Mn on the clay surface. Low-temperature lines exhibited by all samples are due to V *+ or VO 2+ replacing A13+ in the octahedral sheet. Recently, electron spin resonance (ESR) spectroscopy has become an important tool in clay mineral research. A number of clay minerals including micas, vermiculite, kaolinite, illite and smectites have been studied with regard to paramagnetic species, either within the aluminosilicate structure or as an external impurity phase. Information regarding the structure and mobility of some transition metal ions located in the interlayer space of smectites has also been obtained by these techniques. Hall (1980) reviewed the applications of ESR spectroscopy to studies of clay minerals in general. However, only a limite