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analyser A piece of Polaroid in a transmitted- or reflected-light microscope which may be inserted into the light path above the mineral section. When the analyser is out of the path of light through the microscope observations are made in plane-polarized light (PPL); when the analyser is in the path of light, observations are made in crossed polarized light, or crossed polars (crossed nicols, xpols, or XPL). See NICOL PRISM.