Determining the compositional and structural characteristics of pyroxenes in rocks can be crucial to understanding their petrogenesis. Such characterization would also be useful in terrestrial field and laboratory investigations. The detail features in Raman spectral patterns can be used to distinguish among different structures of quadrilateral pyroxene. Raman spectral peak positions are the key to determineing pyroxene cation mole fractions. Note the deconvolved peaks in spectrum a. Correlations are shown among the positions of three Raman peaks and the molar ratios of the three principal cations in pyroxene octahedral sites.
Histograms indicate the number of cases as a function of parameter value.
The lower graphs show the absolute values of discrepancies between Raman and EMP values. These erroneous values are all overestimates and can be detected and corrected because the structural pattern of the spectra allows their identification as low-Ca orthopyroxene. Predicted values obtained from Raman measurements are compared with EMP-determined values of cation mole fraction for equilibrated pyroxenes in two lunar rocks and five terrestrial samples. The monotonic change in position of Raman peak 3 relative to peak 2 is shown. The gap between points for the equilibrated pyroxenes in b indicates the presence of a host pyroxene and exsolution lamellae and identifies the pyroxenes as equilibrated.