A blue fire precious opal stone with blue, green red, and orange play-of-color.

What is Precious Opal? 2


What is Precious Opal?

Precious opal is any type of natural opal gemstone that shows a “play of color,” such as flakes of variable colors reflecting from inside the specimen upon white light exposure. Unlike common opal, a precious stone can reflect multiple colors from a single viewpoint. For an example of an opal stone with a play-of-color, please refer to the photograph below. Updated February 24, 2021.

An example of precious opal with a play-of-color.

An example of precious opal with a play-of-color – Photo: By QualityGems

What is the Play-of-Color in Precious Opal?

The key identifier of a precious opal stone is its play-of-color. By definition, this a prismatic display of each color in the visible light spectrum. To illustrate, human eyeballs are a receptor of electromagnetic radiation. In fact, variable wavelengths upon white light reflection and refraction are what results in one’s ability to identify different colors. As such, when white light reflects upon a precious opal stone, a variety of wavelengths ranging between 400 and 700 nanometers disperse from it. And the outcome is a variety of colors by means of a prism, from the viewpoint of the naked eye.

Prismatic display of each color in the visible light spectrum in Precious Opal. 

Prismatic display of each color in the visible light spectrum in Precious Opal. Photos by: NASA & Australian Opal Direct.

Molecular Structure of Precious Opal

Opal is a mineraloid with a composition of silica spheres and interstitial water molecules. As a result, opal can refract white light into various wavelengths. And in the case of a precious opal stone, there are multiple wavelengths produced at once. The outcome is the “opalescence process,” which demonstrates an array of colors for the human eye. This is similar to the process of white light traveling through a prism.

Molecular Structure Diagram of Silica Spheres Comprising Precious Opal.

Molecular Structure Diagram of Silica Spheres Comprising Precious Opal. Photo BY: Wikicommons.

Precious Fire Opal

Fire opal can be in the form of a precious stone and common stone. And both versions of the gemstone are highly sought after. In fact, opals that show dominant red colorations are rarer than most other colors, due to the chemical structuring of larger silica spheres. As a result, some precious fire opal stones that also reflect blue, green, and purple hues may be less valuable than a common fire opal stone.


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