A technique based on the properties of some anisotropic or birefringent substances (minerals, vitamins, chlorophyll, collagen, etc.).
It is used in specific areas of microscopic analysis, in particular mineralogy, in which case it is possible to collect unique and subjective data for the recognition of the mineral (thanks to the use of polarized light), but also in some applications in biology or medicine (gout analysis, study of cell membranes).

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