Opal and moonstone are both popular gemstones today, though they can be difficult to tell apart.
To help you better understand these two gems, here is everything that you need to know.
Opal vs Moonstone: The Facts Explained
What Is Opal?
The opal is one of the world’s most popular gemstones and it has been held in high esteem since antiquity.
The ancient Romans considered it to be one of the most precious gems due to its ability to contain every color on the spectrum.
Technically, opal is a hydrous silicon dioxide that is amorphous and without a crystalline structure.
This makes it better described as a mineraloid, rather than a mineral.
Opal is also fairly fragile, rated only 5.5 to 6.0 on the Mohs hardness scale.
This means that it can be prone to chipping or scratching if not cared for properly.
There are many different types of opal found across the globe in various deposits.
Australia is one of the most important sources of opal, although Mexico and Ethiopia are both a close second.
In the United States, opal can be found in Nevada, Oregon, Idaho, Louisiana, California, Arizona, and Texas.
The most well-known types of opal include the common opal, fire opal, boulder opal, and precious opal.
Although there are over 19 different types of opal known in the world.
Precious opal is much lauded for its colorful flashes known as “play-of-color”.
This is something that the common opal lacks.
This play-of-color can be noticed when looking at a precious opal under a bright light.
When moving the gemstone, you will notice changes in how the colors ‘move’ within the stone.
Play-of-color is caused by the opal’s internal structure, which contains evenly packed spheres that can cause an effect similar to that of a prism.
Precious opals are extremely rare and only a limited number are found in locations across the world, with most coming from Australia.
The common opal is what most people may mistake as moonstone or vice versa.
This gemstone does not display the play-of-color that its precious variety does, although it is found in many different colors.
Colors of the common opal can include pink, yellow, green, blue, and purple.
While not as illustrious as other varieties, their bright hues can be quite striking.
The white opal is a variation of the precious opal that possesses a white, cream, or yellow color.
This is also the type that many people think of when they hear the word opal.
This was also the kind of opal that was most commonly used in jewelry in the United States until the last few decades.
What is Moonstone?
Moonstone is a type of gem-quality feldspar that exhibits adularescence, a shimmering effect that gives the stone a bright pearly sheen.
This glow was what gave the moonstone its name, as it was likened to the glow of the moon through thin clouds at night.
Adularescence is caused by thin layers of albite and orthoclase which each have varying compositions and refractive properties.
When light moves through these thin layers it is bent, reflected, and then scattered throughout the surface of each layer.
Like opal, moonstone isn’t a very hard stone, rated only between 6.0 and 6.5 on the Mohs hardness scale.
This means that it can be easily scratched by common everyday objects.
Moonstone can also be broken easily by a sharp impact due to having two directions of perfect cleavage.
Moonstone can be found in many different colors, including grey, brown, white, orange, pink, yellow, and green.
Moonstone can also be colorless.
Colorless pieces of moonstone have the potential to produce a blue adulancescence, often called a ‘blue flash’.
These gemstones are extremely rare and desirable.
Today, most moonstone comes from Sri Lanka, although Myanmar, India, and Brazil also produce significant quantities.
Opal vs Moonstone: How Are They Different?
Both opal and moonstone can be found in a plethora of colors, and sometimes they can look similar at a glance.
However, there are some key ways you can tell these gemstones apart.
The Opal is noted for having its unique “play-of-color” effect that can be seen in precious varieties.
Although moonstones can exhibit their own form of this phenomenon, it will often be coupled with a glow effect, and when noted side by side the difference will be evident.
However, because the common opal doesn’t have this effect, you might be unable to determine the difference using play-of-color.
To tell the difference between the moonstone and the common opal, you should instead look at the unique effect of the moonstone.
Adularescence, the simmering effect that we touched on early, isn’t present in any form of opal.
When you look at a moonstone you should notice this shimmering effect coupled with a glow that will seem to be coming from within the stone as it hits and scatters the light.
Look for Layers
Another way to tell an opal from a moonstone is to look for layers.
Because moonstone is comprised of layers of albite and orthoclase, you can often see these layers when examining the stone visually.
This can be another great indication that can help you tell which stone is which.
Watch Out for Opalite
Opalite (also known as opaline) is a manmade glass that is neither moonstone nor opal but is often marketed under those names.
Other names for it can include seal opal or opalite quartz.
One way you can spot this imposter is by noting a few factors.
For one, opalite is often very inexpensive.
It will also have no inclusions and be perfectly clear.
Sometimes you can also spot tiny bubbles inside the glass which can help give it away.
Another way to tell is by examining how it changes when viewed in different ways.
For example, opalite can appear white with gold flecks when placed against light backgrounds, but it will appear to have a bluish hue against a dark background.
Two Stones, Many Varieties
One thing that makes opal and moonstone so difficult to identify is the wide variety that they can come in, specifically opal.
However, by knowing what to look for, you can start to more easily identify these two stones through their visual tell-tale differences.
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