The mere objective of presenting this introduction is to give practical discussion of elementary optics, as applied to Optical Mineralogy. There can be some areas in this site with elaborate discussion in an attempt to present the important details on Optical Mineralogy. Some explanations will also be made as simple as possible by presenting only the optical phenomena of minerals as seen through petrographic polarizing microscopes, while other areas might touch on the theoretical aspects as to the cause of these phenomena.

First, in some ways, we need to know some important aspects of light and its nature. Light may also be regarded as transmitted in straight lines by vibrations of the ‘ether,’ taking place at right angles to the direction of the transmission. The ordinary light is a light with the ether vibrations found in all possible directions, the path described by any particle of ether constantly changing. The plane polarized light on the other hand is simply the light with the ether vibrations all parallel to one plane passing through the direction of transmission.

By experiment, it has been proved that there exists a very close relation between the optical properties of crystals and their other physical properties, such as color, form, transmission of heat, and others. Therefore, it is often possible to determine important crystallographic facts even in the absence of any distinct outline. This can then be done accordingly by careful optical investigation of a crystal section.