Biaxial calcite

Walker and Parsons¹ have called attention to the anomalous properties shown by some calcites probably formed at high temperatures, and they have ascribed these properties to the molecular rearrangement which would take place at the inversion from alpha calcite at 970°. Among these anomalous properties described by them is a biaxial character, and a value of 15° for 2 E. Moreover the calcite does not exhibit complete extinction, possibly, they thought, due to some molecular disturbance.