Undulose extinction

Undulatory extinction ( undulös: wavy ) is a mineralogical term for the partial extinction of a particular mineral under crossed polarized light. The analysis will take place under the polarizing microscope, the mineral is present as a thin section before. Ideally, a mineral has all offset by 90 degrees, a total cancellation of the cross polarized light and at 45 degrees to each of the strongest bleaching. When Undulösen extinction this steady change (every 45 degrees) of Light does not come about after dark, but it comes at a turbulent change. This phenomenon often occurs in tectonically beanspruchtem quartz, while the rock was deformed plastically and the atomic lattice distorted.

Background

When crossed polarized light passes through a transparent anisotropic mineral in the thin section, the light beam in two mutually perpendicular swinging light waves shared with different refractive indices. When the vibration planes of the different vibration planes of the polarizer and the analyzer, the thin section is brightened. In contrast, when the vibration planes are parallel to those of the polarizer and of the analyzer after they have passed through the crystal, then it comes to extinction. If the stage is rotated further, it comes in the analyzer to increasing interference in the diagonal position of the maximum whitening is achieved (45 degrees to the total extinction moved). If one turns the stage now on, the mineral is darkened again and it finally comes to total extinction ( again by 45 degrees to the strongest whitening moved). In plastically deformed minerals, such as Crystal, the atomic lattice is distorted so that the light beams not having a uniform vibration plane and there is undulatory extinction. This is because some of the light is stopped by the analyzer ( vibration plane parallel to the analyzer ) and the other not ( different vibrational level to the analyzer ).