A polarized light microscope magnifies objects invisible or too small to be seen by the naked eye. But unlike its other microscope counterparts which merely magnify the specimen, the polarized microscope provides additional information on the absorption color, boundaries between minerals of differing refracrive indices, and distinguishes between isotropic and anisotropic materials. The polarized microscope has been and is still extensively used in the field of geology. It is invaluable in the study of the properties of minerals in rocks sectioned very thinly. It also allows the study of of industrial and natural materials, whether refined, extracted or manufactured. Its application in the fields of biology and medicine include the analyses of DNA, starch, wood and urea. The technique may be used to measure specific properties (quantitative) or simply describe observed entities (qualitative). Polarized light microscopy makes use of polarized light. In contrast to “common” light that vibrates at right angles to the direction of its path, plane polarized light vibrates along one plane or direction only. This cannot be appreciated by the naked human eye.

Using polarized sun glasses allows the eyes to see light as it travels along a single plane hence reducing the glare usually seen in regular, non-polarized sun glasses. Polarized microscopy exploits the optical properties of anisotropy to unveil detailed data on the structure and basic composition of the materials. This technique is important for diagnosis and identification purposes. Isotropic materials have the same optical properties in any given direction. Examples of isotropic materials are gas, liquid, unstressed glass and cubic crystals. They have only one refractive index and do not restrict the vibration direction of the light passing through them. Anisotropic materials on the other hand have optical properties that vary depending on the orientation of incident light with its crystallographic axes. Their refractive indices are dependent on the direction through which light is propagated in a substance and on the vibrational plane coordinates. Anisotropic materials include ninety percent of all solid substances, their varied refractive indices allow them to act as beam-splitters and divide light rays into two parts. Polarizing microscopy takes advantage of the interference of split light rays because they reunite along the same optical path to gain information about these substances. However, the preparations necessary for viewing the specimens under the polarized light microscope are far more complex than the ones used for ordinary biological specimens. In geological materials, for example, the rocks that have to be viewed under polarized light microscopy must me sectioned into thin pieces to facilitate the passage of light. The process entails that the rock must be sectioned evenly and flawlessly, because nicks on the surface of the specimen will change the data that an observer wants to obtain. Diamond encrusted crushers may be needed to make hard substances smaller, while grinders with varying coarseness refine them. Despite these complexities in specimen preparation, polarized light microscopy remains an unequaled tool in the assessment of materials whether in biology or geology, their optical characteristics and properties.