OPTIC NORMAL OR BIAXIAL FLASH FIGURE

The optic normal or biaxial flash figure is not useful for determining optic sign, because the 2V cannot be determined and it cannot be distinguished from a uniaxial flash figure.

Estimates of 2V angles can be obtained from a centred Bxa figure, for 2V < 40°, and from a centred optic axis figure for 2V = 0 to 2V = 90°, (See Figure 7.32. in Nesse).