Analysis of peak positions vs. structural changes suggests that for the M2 polyhedron, in which
Ca substitution for Mg occurs, a different deformation mechanism acts in Ca richer and poorer P21/c
pyroxenes, and that Ca richer P21/c pyroxenes deform with the same mechanism as C2/c pyroxenes.
The frequency of the peak at 670 cm–1 was found to change linearly with the kinking angle of the
tetrahedral chains for C2/c and of the B chain for P21/c, whereas the position of the peak ascribed to
the A chain was little affected by the kinking angle.