Abstract: A pocket polarization-magnifying-lens is designed, based on Brewster's law. This instrument can be used for the following purposes: (1) to examine "crystallinity" by observation of double refraction effect; (2) to ascertain whether the sample extincts straightly or not, as well as whether the sign of elongation is positive, negative or variable; (3) to determine the approximate range of refractive indices N₁ & N₂ by immersion method. This instrument is profitable for field observations, because of light weight, simple construction and essiness in operation. No artificial illumination is needed for operation.