Opal Grading

Opal Grading

Precious opal is a beautiful stone that displays a rainbow of colors within. Opals can come in a variety of hues, including white, black, blue, and colorless, all with prismatic colors and fire. October claims the opal birthstone and an opal stone is a common gift on a couple's 14th wedding anniversary. Purportedly, the stone brings good fortune and has been long associated with royalty. Its beauty makes it ideal for use in an opal ring, an opal necklace, and all manner of eye-catching jewelry.

How Are Opals Graded?

There are two different types of opals, common opals and precious opals (sometimes called noble opals). Precious opals are most commonly used for opal jewelry. They are available in a few different colors. However, their rainbow display of fire makes them precious and unique.

It's this "play-of-color" on which opals are graded. Unlike other stones graded on their carat weight or clarity, opal color reigns supreme when determining this stone's quality. Other considerations include flaws, size, and transparency.

How to Grade Opal Color

Natural opals can be found worldwide and come in the following colors, white, yellow, grey, black, or brown. However, these colors can mean little to the grading of the stone, as opal is rarely a single color. What graders are looking for is the prismatic rainbows displayed within the body of an opal and how dense and intense these colors are.

This is commonly known as "play-of-color" and refers to how many hues can be found in the opal. Cooler shades like blue and green are common, making them less valuable. Warmer tones like yellow, pink, and orange are rarer and, therefore, more valuable. Pure red is traditionally the most sought-after, with pink being a close second. These colors can flash when the stone is turned, making opals tricky to grade. Often, a grader will decide on a dominant color, affecting the price and value the most.

Less concern is paid to the background color of the stone, though black, electric blue, and red opals tend to be more sought after than other colors.

How to Grade Opal Clarity

Opal clarity focuses on two things, appearance, and flaws. Saturation, hue, and tone affect the opal's clarity grade. For example, a brilliant bright blue stone, sometimes called electric blue, will be more valuable than a pale or milky blue stone.

Additionally, inclusions and flaws can affect clarity. The stone's transparency can also determine a clarity grade, as it can make defects more or less visible. Here are a few of the more common inclusions you make come across in an opal stone.

Common Inclusions:

• Fractures: small cracks or breaks in the stone.

• Sand: deposits or pockets of sand within the stone.

• Chips: a nick or dent caused by missing material found at the edge of the stone.

• Sandstone: when opal(s) are trapped within the sandstone.

Less Common Inclusions:

• Potch lines: potch is the mineraloid (silica) that opals are formed on. Sometimes lines or areas of potch can remain, meaning there is an absence of opal.

• Vegetation, vegetation pattern, or phantom inclusions: where the opal has replaced plant matter found within the potch, and the foliage is now trapped inside the opal, or a shadow of the vegetation remains (common with Ethiopian opal).

The Opal Grading Chart

Opals are often assigned one of the following quality grades.

Heirloom (AAAA)

These opals will often be milky but have an intense play-of-color. They're surface clean without visible inclusions and opaque. Only around 1% of opals belong to this category.

Best (AAA)

Opals in this category will have a medium play-of-color instead of high but a similar milkiness. They're opaque with very few surface flaws. This category applies to the top 10% of opals.

Better (AA)

33% of the top opals will be in this category. Like the other ratings, they are opaque and milky. However, they have only a low play-of-color and few or slight surface flaws.

Good (A)

Around 75% of opals will receive a rating of good. They're milky and have no play-of-color. These stones will be opaque but will have visible surface blemishes.

More about Opal Grades

Opals naturally come in various sizes, so carat weight often isn't an issue. However, opals will be given a price per carat, which means larger opals will cost more. In addition, these stones can have various body tones, patterns, and brightness levels, each with a different rating scale.

Unlike other gemstones, opals are not faceted. Opal jewelry will often feature a cabochon opal, meaning it has been cut into a rounded shape and set into jewelry such as opal earrings or an opal bracelet.

Why Not Treat Yourself to an Opal?

Opals are beautiful stones that typically go with any outfit and style due to their array of colors. Their rainbow fire and brilliance are unmatched, making them excellent for various jewelry pieces. Available in a variety of sizes and shapes, you can easily find the perfect one-of-a-kind opal to add to your jewelry collection.


Which is the best quality grade for an opal?

The best quality grade for opal is heirloom or AAAA. However, only the top 1% of opal stones receive this designation.

What is the meaning of an AAAA opal?

AAAA or heirloom is the top rating an opal can receive. The stone is milky, opaque, and surface clean with a high play-of-color.

AAAA or heirloom is the top rating an opal can receive. The stone is milky, opaque, and surface clean with a high play-of-color.

What is play-of-color in an opal?

Play-of-color is the term given to how an opal uses and interacts with light to create a spectral flash of colors, much like a rainbow.

How to judge if an opal is valuable?

Opals are graded on a few factors, most notably color, play-of-color, and clarity. Black opals (those with a dark body tone) with a high play-of-color on their surface are often the most valuable. You should also look for signs that convey your opal is natural and not synthetic. Such as by checking if it has layers, as if a thin slice of precious opal was attached to a black backing material, which is common with synthetics.

4.8 Google review stars

Read our reviews