Extinction (optical mineralogy)

Extinction is a term used in optical mineralogy and petrology, which describes when cross-polarized light dims, as viewed through a thin section of a mineral in a petrographic microscope. Isotropic minerals, opaque (metallic) minerals, or amorphous materials (glass) show no light (i.e. constant extinction). Anisotropic minerals will show one extinction for each 90 degrees of stage rotation. Extinction is a term used in optical mineralogy and petrology, which describes when cross-polarized light dims, as viewed through a thin section of a mineral in a petrographic microscope. Isotropic minerals, opaque (metallic) minerals, or amorphous materials (glass) show no light (i.e. constant extinction). Anisotropic minerals will show one extinction for each 90 degrees of stage rotation.