A dichroscope is an essential tool for gemologists, allowing them to observe whether a gemstone exhibits dichroism (showing two colors). This is particularly useful for differentiating between stones of the same color. The dichroscope splits light into two polarized rays, each vibrating at right angles to the other. This separation reveals the pleochroic colors of doubly refractive stones, while singly refractive stones display a single color.

By viewing the gemstone from various angles, gemologists can see the two pleochroic colors side by side and assess the stone's dichroic properties. For trichroic gems, three distinct colors will be visible when viewed from three perpendicular directions.