Opalescence or play of color is an optical phenomenon associated with the mineraloid gemstone opal,[opalescent. 2019. In Noah Webster'
]
/ref> a silicon dioxide.
Definition
Each of the three notable types of opalprecious, common, and fire[
/ref>display different optical effects; therefore, the intended meaning varies depending on context.
]
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The general definition of opalescence is a milky iridescence displayed by an opal, which describes the visual effect of precious opal very well, and opalescence is commonly used in lay terms as a synonym for iridescence.
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In contrast, common opal does not display an iridescence, but often exhibits a hazy sheen of light from within the stonethe phenomenon that gemologists strictly term as opalescence.
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Fire opal is a relatively transparent gemstone with a vivid yellow-orange-red color and rarely displays iridescence.
Mechanism
The optical effects seen in various types of opal are a result of refraction (precious and fire) or reflection (common) due to the layering, spacing, and size of the myriad microscopic silicon dioxide spheres and included water (or air) in its physical structure.[Smigel, Barbara W. 2012. Optical Phenomena in Gemstones. In Introduction to Gemology. Retrieved January 8, 2019, from http://www.bwsmigel.info/Lesson6/DE.Optical.Phenomena.html]
In a physical sense, some cases of opalescence could be related to a type of dichroism seen in highly colloid with little opacity. Due to Rayleigh scattering, a transparent material appears yellowish-red in transmitted white light and blue in the scattered light perpendicular to the transmitted light.
Fluids
In fluids, the near the gas-liquid transition, the substance can become cloudy. This phenomenon is called critical opalescence.
See also
