Aquamarine Color and Heat Treatment


“Aquamarines,” Brazil, by Mauro Cateb is licensed under CC By 2.0
“Aquamarines” by Mauro Cateb is licensed under CC By 2.0

One of the most popular misconceptions about aquamarine is that its color should be just blue. Most consumers do prefer a dark blue aquamarine color. However, natural, untreated aquamarine is gemologically described as a transparent, blueish green variety of beryl. Let’s examine that “blueish green” color and how heat treatments affect it.

What is Natural Aquamarine Color?

Personally, I would describe an aquamarine’s color based on the stone’s body color and highlights. Those with blue body color and sea green highlights have “aquamarine color.” Those with green body color and blue highlights have “sea foam color.” Both these colors are gorgeous. I sell them quite well, mainly because many jewelers have never seen these colors and want something different and new. Some don’t even recognize the stones as aquamarines.

Although some aquamarine gemstones come out of the ground blue, almost all of them start life blueish green. Most of these are heat treated to blue, since this is the color the buying public prefers. Times and tastes do change, however. Natural color aquamarines are selling quite well. (I prefer them unheated, too).

“Beryl v. Aquamarine” by Ed Uthman is licensed under CC By 2.0
“Beryl v. Aquamarine” by Ed Uthman is licensed under CC By 2.0

Think Before You Heat Aquamarine

I strongly recommend that you leave aquamarine heat treatments to the experts. Although aquamarine is generally easier to heat than most other materials, the results may not be what you want. Consider these points:

  • Most commercially available aquamarines are already heated. They can even be treated at the mine before they reach the market. This applies to finished stones as well as rough.
  • Not all aquamarine can be heated successfully. Stones from some sources will crack and break apart during treatment and thus aren’t normally heated.
  • In general, aquamarine is usually under stress along the length of the crystal at about a third to the middle of its thickness. Beryl tends to crack lengthwise. Since most aquamarine isn’t that big around, yields and stone sizes will decrease dramatically when it cracks.
  • Seeing green in rough beryl doesn’t necessarily mean the stone is unheated. Stones from some locations retain some green color even when heated successfully.
  • Heating an aquamarine with a flaw, bubble, or inclusion will usually make the problem grow. Even if you only see a hint of a flaw, that may indicate there are problems in the stone you can’t see.

If you choose to heat treat aquamarine yourself, it’s important to know the source of the rough. You’re taking a chance when you heat unknown rough.

Aquamarine Color: Before and After Heat Treatment

Natural aquamarine crystal.

This is a nice, unheated, natural aquamarine crystal. Its color is definitely a little on the green side. I would call this “sea foam color” rather than “aquamarine color.” Natural, unheated rough is rather hard to find. It took me a while to get some material I could heat so I could write this article. Please note: I knew where this material was mined and that it would actually heat without problems. Without this information, I wouldn’t have heated this rough.

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Sawing a natural aquamarine crystal.

I sawed the crystal almost in half. I found a slight flaw in the stone a little over halfway from the left in the picture above.

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Sawed, natural aquamarine crystal.

I decided to heat one half of the crystal and compare its color to the unheated half. This would be a good way to compare the effect of heating on aquamarine color.

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Comparison of treated and untreated aquamarine pieces cut from the same stone.

Magic! The heated half now has that blue aquamarine color most people are used to seeing. The stone was heated at 400° C for an hour or so. The color change was fairly dramatic. However, note that the blue color is no more saturated than the original blueish green color of the natural crystal. Heating changes the color but doesn’t affect the saturation.

Is It Better Not To Heat Aquamarine?

If there is greater demand for blue aquamarine, doesn’t it make economic sense to buy unheated aquamarine rough at bargain prices and make a killing after heating it?

Unfortunately, selling your treated aquamarine may not make the killing you’d expect.

“Aquamarine; blue beryl” by Decym92. Public Domain.
“Aquamarine; blue beryl” by Decym92. Public Domain.

Rough dealers and miners routinely heat aquamarine before it enters the general market. Nevertheless, the cost of heated and unheated rough is the same. If someone tries to sell you blueish green rough cheaply and assures you it will “heat blue,” buyer beware. The reason the rough is still blueish green may be because it can’t be heated successfully.

(Editor’s Note: Beware of stones sold as “white aquamarines,” which are not aquamarines but colorless beryls).

Even if you find unheated rough and successfully heat it blue, you’ll be competing with commercial sellers of blue stones. You most likely won’t have the volume to compete with them successfully. On the other hand, if you cut natural, untreated aquamarine, you’ll have something out of the ordinary. You’ll do better if you’re not competing with commercial sellers, at least color wise. Untreated aquamarines have an underserved market. I personally have better luck with unusual stones and generally can get more money per carat for them.

You can cut beautiful gems out of untreated aquamarines. Heat treating aquamarines is an unpredictable process. You may ruin a good stone for nothing. Even if the stone doesn’t crack, you may not be happy with the resulting color.

There are good reasons for the small scale gem cutter not to heat aquamarine. If you still want to try it, good luck.

This bracelet, inspired by the colors of Antarctica, features iolites, moonstones, rock crystals, and chunks and disks of pale blue aquamarine. “Glacial Bracelet” by Marianne Madden is licensed under CC By-SA 2.0
This bracelet, inspired by the colors of Antarctica, features iolites, moonstones, rock crystals, and chunks and disks of pale blue aquamarine. “Glacial Bracelet” by Marianne Madden is licensed under CC By-SA 2.0

About the author
Jeff R. Graham
The late Jeff Graham was a prolific faceter, creator of many original faceting designs, and the author of several highly-regarded instructional faceting books such as Gram Faceting Designs.
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