Ferroelastic phase transition along the join CaAl₂Si₂O₈ -SrAl₂ Si₂O₈

A representative series of feldspars of composition Ca_1-xSr_xAl₂Si₂O₈ has been synthesized. The cell parameters have been measured as a function of composition, and a continuous ferroelastic transition from monoclinic to triclinic observed at Ca_0.09Sr_0.91Al₂Si₂O₈ on increasing Ca content. Ferroelastic and coelastic strains arise in the triclinic phase and indicate that the transition may be modeled in terms of coupled order parameters (primary ferroelastic and secondary coelastic) within the framework of Landau theory. The primary order parameter suggests behavior according to a second-order model. -Authors