A C2/c to P21/c phase transition in pyroxenes occurs between augite and pigeonite because of the substitution of Ca
by Fe
and/or Mg. Studies on the compositionally induced C to
P phase transition in quadrilateral pyroxenes are difficult due
to the presence of a wide miscibility gap between Ca-rich and
Ca-poor clinopyroxenes: natural intermediate samples, namely,
subcalcic augite, are invariably affected by some kind of exsolution textures. Exsolution gives broader and less resolved Raman
peaks but can provide potential information on the microstructure
of pyroxenes.