Fourier Transform R a M a N Spectroscopy of Kaolinite, Dickite a N D Halloysite

-The vibrational modes of clay minerals are uniquely accessible to FT Raman spectroscopy, but this potentially powerful technique has found limited application to the study of clay mineral structure. Raman spectra in the 50 to 3800 cm-t region were obtained for a number of kandite clays. The kandite clay minerals are characterised by relatively intense bands centred at 142.7 cm -I for kaolinite, 143 cm -~ for halloysite and 131.2 cm-I for dickite with prominent shoulders at 129, 127, and 120 cm1 respectively. These vibrational modes are attributed to the O-A1-O and O-Si-O symmetric bends. Differences in the lattice modes for the kandite clay minerals in the 200 to t200 cm -I were obtained. Four OH bands were obtained for kaolinite 3621, 3652, 3668, and 3695 cm-1; three OH bands were found for a selection of dickites and halloysites. The San Juan Dickite and the Eureka Halloysite show further resolution of the low frequency 3620 cm -1 hydroxyl band. This splitting is attributed to variation in the position of the inner hydroxyls. Variation in band intensity and position was found to be sample dependent. Key Words--Dickite, FT Raman spectroscopy, Halloysite, Infrared spectroscopy, Kandite clay, Kaolinite. I N T R O D U C T I O N Vibrational spectroscopy in particular has been widely used for the study of clay mineral structure for a very long period of time (Lazarev 1972, Farmer 1974). Definitive analysis of the IR spectra has enabled structural analysis to take place. Recently infrared emission spectroscopy has enabled the clay mineral structure at elevated temperatures to be measured in situ (Vassallo 1992, Frost 1994, 1995). The Raman spectroscopy of clay minerals has received less attention (Wiewiora 1979, Johnston 1985, Pajcini 1994). The reason why Raman spectroscopy has received less attention is the weakness of the Raman scattered signal, the photodegradation of the sample and the occurrence of fluoresence which swamps the signal. More recently the advent of FT Raman spectroscopy (Chase 1986, Cutler 1990) which uses near infrared radiation as the excitation source and a Fourier Transform spectrometer enables the study of clay mineral structure to be further investigated. The use of FT Raman spectroscopy offers the advantages of reduced fluoresence, improved signal to noise by coadding of scans and the longer wavelength of light reduces sample degradation.