Becke line test
The Becke line test is a technique in optical mineralogy that helps determine the relative refractive index of two materials. It is done by lowering the stage of the petrographic microscope and observing which direction the light appears to move. This movement will always go into the material of higher refractive index. This index is determined by comparing two minerals directly, or comparing a mineral to a reference material such as Canada Balsam or an oil of known refractive index.
The method was developed by Friedrich Johann Karl Becke.
