Autocorrelation analysis of infrared spectra from minerals

The autocorrelation function. Corr(alpha,omega') =integral(-infinity)(infin ity) alpha(omega+omega')alpha(omega)d omega, may be used ra parameterise ef fective line widths of absorption bands in IR spectra. It has the advantage of not requiring any peak fitting to the primary spectra and can be applie d to individual bands or groups of bands in a spectrum. A new procedure for analysing autocorrelation spectra which result from the application of the autocorrelation function to primary spectra is presented. The approach is well suited for quantifying line width variations in powder absorption spec tra from sequences of samples with varying composition, degree of cation or der or structural state. Worked examples are set out to illustrate differen t applications of the approach, including the characterisation of structura l phase transitions in tridymite, Al/Si ordering under non-equilibrium cond itions in Mg-cordierite, shea range Al/Ge order in BaAl2Ge2O8 feldspar and mixing behaviour in the jadeite-augite solid solution.