A note on Bekke's method for comparing the refractive index values of neighboring mineral grains in thin sections

Abstract

This method, proposed by Bekke in 1893, has become widespread. As is known, it is based on observing the movement of a light strip that appears when using strong lenses at the boundary of neighboring mineral grains, if you move the microscope tube, focusing it either on the upper (upper setting) or on the lower surface of the section (lower setting).