Polarized light microscopy is a non-destructive technique which uses plane-polarized visible light to interrogate samples. The polarization of the light source leads to enhanced image contrast in materials that have directionally-dependent refractive indices (birefringent).  In PLM, light passes through a polarizer prior to interacting with the specimen and through an analyzer before reaching the observation optics (either eyepieces or camera). The morphological character of a sample may be obtained by PLM as well as information about homogeneity, crystal structure, origin (natural versus synthetic). Additionally, with the addition of components such as hot stages and index matching oils, the refractive index of materials may also be determined by PLM.  While most broadly used in the fields of geology and materials science, PLM can also be applied to forensic, pharmaceutical, and biological samples as well. The combination of information obtained from PLM alone can often be used to identify unknown materials. Some microscopes can be coupled to cameras for image preservation. Microscopes are typically employed as benchtop instruments.  It is an extremely mature analytical technique and instruments are widely available from a large number of manufacturers.  Microscope prices vary widely depending on the quality and complexity of the lens optics and accessories such as camera and hot stages.