Let us consider critical points lying on the bisectrix. All these points are of the form (x, x) and x can be found from (4.2)
In contrast to system (3.2) which may have critical points only of the form (x, x) system (4.1) may have critical points also aside of the bisectrix.
There is also a critical point (0.06407,0.06407) on the bisectrix.
Therefore the types of both critical points aside of bisectrix are stable nodes.
The optical orientation, identical to that of olivine, is a = Z, b = X, and c = Y, which agrees with Payne's observation that the optic plane parallels the base and that the acute
bisectrix is parallel to b.