Opalescence refers to the optical phenomena displayed by the

mineraloid A mineraloid is a naturally occurring mineral-like substance that does not demonstrate crystallinity. Mineraloids possess chemical compositions that vary beyond the generally accepted ranges for specific minerals. For example, obsidian is an amor ...

gemstone A gemstone (also called a fine gem, jewel, precious stone, or semiprecious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, ...

opalopalescent. 2019. In Noah Webster's 1828 American Dictionary of the English Language. Retrieved January 7, 2019, from https://1828.mshaffer.com/d/word/opalescent (hydrated silicon dioxide).Opal Gemstone Information. 2018. In Gemstone Select. Retrieved January 8, 2019, from https://www.gemselect.com/gem-info/opal/opal-info.php However, there are three notable types of opal (precious, common, and fire),Douma, M., curator. 2008. Opal. In Cause of Color. Retrieved January 8, 2019, from http://www.webexhibits.org/causesofcolor/15F.html each with different optical effects, so the intended meaning varies depending on context: * Precious opal. The general definition of opalescence is a milky

iridescence Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear to gradually change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, feathers, butterfl ...

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

. * Common opal. In contrast, common opal does not display an

but often exhibits a hazy sheen of light from within the stone—the phenomenon that gemologists define strictly as opalescence."Opal Description". 2019. Gemological Institute of America. Retrieved January 8, 2019, from https://www.gia.edu/opal-description. This milky sheen displayed by opal is a form of

adularescence Adularescence ( ) is an optical phenomenon that is produced in gemstones like moonstone. The optical effect is similar to labradorescence and aventurescence. Description The effect of adularescence, also commonly referred to as ''schiller'' or ...

. * Fire opal is a relatively transparent gemstone with a vivid yellow-orange-red color and rarely displays iridescence. 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. When the size and spacing of the silica spheres are relatively small, refracted blue-green colors are prevalent; when relatively larger, refracted yellow-orange-red colors are seen; and when larger yet, reflection yields a milky-hazy sheen.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 Why is the sky blue

In a physical sense, some cases of opalescence could be related to a type of

dichroism In optics, a dichroic material is either one which causes visible light to be split up into distinct beams of different wavelengths (colours) (not to be confused with dispersion), or one in which light rays having different polarizations are abs ...

seen in highly dispersed systems with little

opacity Opacity or opaque may refer to: * Impediments to (especially, visible) light: ** Opacities, absorption coefficients ** Opacity (optics), property or degree of blocking the transmission of light * Metaphors derived from literal optics: ** In lingu ...

. 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. The phenomenon illustrated in the bottom photo is an example of the Tyndall effect.

References

{{Reflist Optical phenomena

See also

References