The dichroscope is the preferred type of instrument to inspect gemstones with pleochroisms. A calcite rhomb (Iceland spar) separates the polarized light rays that pass through the gemstones and displays the pleochroism on viewing screens. Dichroscope is usually used to identify gemstones that are transparent and isotropic. When using a dichroscope, the gemstones are constantly turned until two colors with the biggest differences show up on the windows; for gemstones with weaker dichroism, a polariscope should be used in conjunction with the dichroscope to further identify the stone.