Iridescence – A Visual Feature of Minerals
In gemology, iridescence refers to the shimmering of gemstones in the colors of the rainbow. The term is derived from the ancient Greek word iris (rainbow); in Greek mythology, Iris was also the name of the personification of the rainbow, who also acted as a messenger of the gods. The colors of an iridescent gemstone differ depending on the viewing angle. This effect is caused by the fact that the light rays are refracted to different degrees by the different thicknesses of the almost transparent layers when they fall into the mineral. The iridescence depends on the layer depth as well as the angle of incidence and the wavelength of the reflected light rays. Due to the natural unevenness of the different layers of the gemstone, its iridescence appears in a variety of color gradations and patterns. The special appeal of iridescence is that the bright colors are shown to their best advantage through their intense sparkle - this leads to the great popularity of minerals and gemstones in which this optical phenomenon can be observed.
The iridescence of gemstones – pearls, labradorite, hematite
A colorful iridescence can be observed in hematite and rock crystal, for example; in fire agate this phenomenon occurs in various shades of brown.
Labradorite exhibits a special iridescence in metallic tones, which is also known as labradorization.
The soft, silky shine of pearls is also due to a special form of iridescence. The light refracts on the layers of mother-of-pearl, creating a shimmer in the colors of the rainbow.
Pearls in the Lexicon
Optical phenomena
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