Raman spectroscopic study of glasses on the join diopside-albite

Abstract Raman spectroscopy has been used to study the structural variation of a series of glasses along the join diopside-albite. The spectra show that these compositions can be characterized by a smooth and continuous variation in silicate speciation as a function of composition. However, the presence of three discrete bands in the low frequency region of intermediate composition glasses at 642 cm −1 , 580 cm −1 , and 470 cm −1 , which change only in relative intensity and not in frequency, argues that the change in speciation is accompanied by the formation of molecular clusters. The 642 cm −1 and 470 cm −1 bands suggest structures similar to the end-member components Di and Ab, while the 580 cm −1 band is interpreted to have a structure similar to a disilicate. There is no evidence for significant Si/Al mixing on tetrahedral sites with non-bridging oxygens, nor is there any evidence that Ca and/or Mg charge-balance Al in preference to Na. These observations should be taken into account to more accurately model the entropy of mixing of diopside-albite solutions.