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How Many Types of Opal are There?

Updated on June 21, 2017

Opal is a form of silica that is considered a mineraloid, rather than a mineral, because it lacks an orderly crystalline structure. However, according to the experts at Auction King, this characteristic is exactly what makes precious opal a desirable gemstone, because light diffracting through the layers of silica is what creates the distinctive shifting rainbow colors (known as “play-of-color”) that opal is known for. The stone can be transparent to opaque, and the base color can range from white to nearly black.

If you’re in the market for an opal, you may justifiably be confused by the plethora of terms used to describe the different varieties of this gemstone. It doesn’t help that some of these terms describe the color of the stone, others its clarity, and yet others its relationship to its host rock. Here is a quick primer to help you distinguish the primary types of opal.

Natural Opal

An opal not treated or artificially altered except by cutting or polishing. These are more valuable than synthetic opals or doublet or triplet opals, where a thin layer of precious opal is combined with other materials to create a finished stone.

Crystal Opal

An opal with a transparent to semi-transparent body. The transparency of these stones tends to allow for a greater display-of-color, which makes them more valuable than opaque opals.

Light or White Opal

An opal with a base tone that is colorless to medium grey. These are the most common, and tend to have a pastel-hued play-of-color. White opals are those with a milk-colored body tone.

Dark or Black Opal

An opal with a base tone from dark grey to black. These are more valuable than lighter-colored opals because they tend to display a more vibrant play-of-color.

Fire Opal

A transparent to translucent opal with a background color of red, orange, or yellow. These stones may or may not exhibit play-of-color; when they do not, they are sometimes referred to as jelly opals. (Note: while you may find the term “fire opal” being applied to any opal that displays a red tint or reddish play-of-color, it properly refers to the stone described here.)

Boulder Opal

An opal that includes its host rock as part of the gem as a backing, as opposed to a solid opal, which is composed solely of opal itself.

Matrix Opal

A stone where opal has filled in pores or holes in the host rock. In the case of both boulder and matrix opals, these stones can be cut and polished to form unique and striking pieces.

Considered good luck in many cultures, opals are a fine addition to anyone’s jewelry collection. Whether you’re looking for a necklace, pendant, bracelet, or ring, you can find a tempting selection at online auctions for below-market prices. With this guide, you can find the perfect opal just for you or your loved one!

Which Opal is Your Favorite?

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