In this method, two matched 1/4 wave plates are used. One is inserted between the polarized and the specimen, the other between the specimen and the analyzer. The 1/4 were plate vibration directions are at 90° to each other and at 45° to the polarizer and analyzer vibration direction. The light is still polarizer, but the effect is that all extinction phenomena of anisotropic minerals disappears. Mineral grains show birefringence independent of their orientation. Only isotropic minerals, minerals viewed along their optic axis and voids appear black.

The benefit of this method is that only voids and a few minerals appear black. The stage need not be rotated to determine whether a black area is a void or a mineral at the extinction position. Circular polarized light is useful for photographing certain features and distinguishing some fabrics. The disadvantage is that certain diagnositc optical characteristics are not visible.

This page (http://www.ces.ncsu.edu/plymouth/programs/circular.html) created by
Vera MacConnell, Research Technician, I on November 17, 1997.
Last Updated on November 17, 1997.