Order-disorder and the high-pressure P1-I1 transition in anorthite

A study on the P1-I1 transition of anorthite having the same composition but with different states of A1,Si disorder is discussed. Transition behavior changes of anorthites subjected to high pressure are thermodynamically analyzed. Results show changes in both the transition character and the P1-I1 transition pressure accompanying A1,Si disorder. These changes are induced by a decrease in the length of the correlation of the state of A1,Si order.