This sometimes shows variations in the colour and relief of minerals depending upon their orientation, but is superficially similar to what would be seen in normal light. Theoretically, crossed nichols with no specimen would result in no light reaching the camera, but many types of crystals effectively rotate and slow the light depending upon the relative orientation of the crystal lattice. Depending upon orientation, this results in interference colours, as the light travelling along different directions in the lattice interferes upon exiting the crystal. The interference colours, relief, and other optical properties are specific to the crystal lattice parameters, and, therefore, the type of mineral and the orientation of its crystals. These two illumination modes enable the precise identification of minerals by transmitted light optical properties.
Similar properties are also useful in reflected light.
Terminology and explanations have been simplified for this presentation. Look up an optical mineralogy text if you are interested in more detail. Imaging Images were digitized using a video camera attached to a Leitz Orthoplan petrographic microscope. This is the same procedure as used for the examination of specimen EC96-001. Images at the same magnification are directly comparable.