A polarizing microscope is a microscope that is mainly used in geological studies to study geological specimens. For this reason, it is also known as a petrographic microscope. It is used in other scientific fields such as medicine and biology as well.
Polarizing microscopes are built like a regular optical microscope but are fitted with some extra features. Unlike regular microscopes that use normal light, a polarizing microscope uses polarized light to study specimens. In polarized light, the light waves vibrate in one direction; in normal light, the light waves vibrate in random directions.
Polarized light cannot be seen by human eyes in normal circumstances. It can, however, be used in polarized light microscopy to highlight features of minerals and other materials. A polarizing microscope uses the birefringent optical properties of anisotropic materials to study them.
Anisotropic materials are solid substances that have several refractive indices; isotropic materials, which include gases and liquids, have only one refractive index. Birefringence or double refraction occurs when a light wave passing through an anisotropic material is split into two rays of differing velocities.
Geological specimens are pared or ground into thin sections for study. The specimen to be studied is placed on a slide on a rotatable specimen stage. The specimen is then illuminated by a light source under the specimen stage.