D. Centered Optic Axis Figures

Because the 2V of olivine is very high (>60), a Bxa figure will not help you in determining the 2V of this mineral. However, the curvature of the isogyres method will enable you to determine the 2V (see handout).

1. Estimate the 2V of olivine BH250-4 (Ask your TA to show you this mineral) using the curvature of isogyres method. Draw the interference figure you see at 45 degrees off extinction showing the location of the optic axis.

What is the maximum birefringence of olivine?

What is the interference color observed for the grain you measured the 2V on? Is it the highest, an intermediate, or lowest interference color observed for olivine?