Pleochroism is a phenomenon in which a gemstone exhibits different colors when viewed from different angles. It is caused when a compound has different absorption spectra for light that is polarized in different directions. For example, when viewing a blue sapphire, it may look blue when viewed from one direction and purple from another. This is because the crystal structure of the stone causes the light to be refracted differently in certain directions. Pleochroism can be used to identify certain gemstones, and some gemstones are valued more highly due to their pleochroic properties.
