Aquamarine is a member of the beryl family. This stone is known for its blue to blue-green color. The name comes from the Latin for “sea water,” and aquamarine folklore is usually tied to sailors and the sea. Aquamarine is the birthstone for March and it’s a popular gem that wears well, is readily available, and moderately priced.
Since aquamarines are available in large sizes, there is no incremental increase in value per carat for large gems. A 50-carat aquamarine will be worth the same price per carat as a single carat gem of equal quality. The gem price is dependent on clarity, depth of color, and to a lesser extent the purity of color.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Is a Variety of||Beryl|
|Colors||Blue to blue-green.|
|Hardness||7.5 - 8|
|Specific Gravity||2.66 - 2.80|
|Stone Sizes||Aquamarine is available in a remarkable range of sizes. Gems have been cut that weigh several hundred carats, much too large to be worn. (See below).|
|Spectral||Natural aquamarine: a broad band at 4270 and a diffuse band at 4560. (Weak band may be seen at 5370). Maxixe aquamarine: a narrow line at 6950, a strong line at 6540 and weak lines at 6280, 6150, 5500 and 5810.|
|Enhancements||May be heat treated to remove green tint. Very common, undetectable.|
|Special Care Instructions||None|
|Formula||Be3Al2Si6O18 + Fe|
|Pleochroism||Natural aquamarine: blue/colorless (sometimes greenish). Maxixe aquamarine: non-pleochroic (blue/blue).|
|Optics||RI: o = 1.567-1.583; e = 1.572-1.590; Uniaxial (-)|
|Etymology||From the Latin aqua marina for "sea water," in allusion to the color.|
|Occurrence||Granitic rocks, especially granite pegmatites.|
|Inclusions||Long, hollow tubes, negative crystals, chrysanthemums. 3-phase, crystal inclusions that are transparent and metallic. Crystals of biotite, phlogopite, rutile, pyrite, hematite, and ilmenite in skeletal crystals. Some stones contain "snow-stars," irregular shaped liquid droplets in a star formation.|
This beautiful gem receives its coloring from trace amounts of iron. The color can be very light to moderately dark. You’ll rarely see an aquamarine darker than a Swiss blue topaz. When you do, the color is usually enhanced by the cut.
When cutting aquamarine, the primary consideration should be depth of color. Deep designs, like barions and emerald cuts, are usually preferred. Faceters should use 43° pavilion mains on aquamarine for the highest brilliance. Low crown angles will produce higher brilliance, but higher crowns are often used to deepen the color.
Beryl gems like aquamarines are some of the easiest gems to polish, with diamond being the most common method. A high quality polish can give light aquamarines such great brilliance they might be confused with higher RI gems. Even with a moderate dispersion of .014, light stones with high crown angles will show their spectral colors well. This makes for an outstanding gemstone. While the highest values go to the richer colors, a well-cut light aquamarine is one of the most spectacular examples of the gem world.
An interesting feature of this gem is its inclusions. Beryl, and aquamarine in particular, are known for having long, hollow tubes. This is a distinctive feature and will identify a gem as a member of the beryl family.
If there are enough of these hollow tubes, cat’s eyes or stars can be produced with proper cutting. A cat’s eye aquamarine is a thing of beauty and is highly prized by collectors. Prices will be very close to that of a clean, faceted gem with the same coloring. Star aquamarine is even more rare than a cat’s eye and can demand a premium price.
The Martha Rocha aquamarine has notable “snow-star” inclusions.
In the 1970s, a very dark blue aqua called the Maxixe aquamarine came on the market. (That is pronounced ma-she’-she.) This is an irradiated product, and the color isn’t stable. These have mostly disappeared from the market, but if you’re ever offered a very deep blue aquamarine, be cautious. You can distinguish the Maxixe from a natural aquamarine by its lack of pleochroism. In natural aquamarine there is distinct blue and colorless dichroism. The Maxixe has no pleochroism and is blue in every direction. The absorption spectrum of natural aquamarine and the Maxixe also differs. With a spectroscope you will see a narrow line at 6950, a strong line at 6540 and weak lines at 6280, 6150, 5500 and 5810. This is considerably different than natural aqua’s spectrum with a broad band at 4270 and a diffuse band at 4560.
You can also distinguish a Maxixe aquamarine from a natural stone with a dichroscope. Both windows remain blue when viewing a Maxixe, whereas one window should be colorless or pale yellowish when viewing an untreated specimen.
Most aquamarines come out of the ground with a greenish tint. This will disappear, leaving a pure blue color by heating to 375° centigrade. Heating aqua to remove its green tinting is very common. In the past this was done routinely. Nowadays, a more sophisticated public is starting to appreciate the slightly green gems free of heat treatments. However, this process is impossible to distinguish, so pure blue aquamarines are described as “probably heat treated.”
- Maine; North Carolina; Mt. Antero, Colorado.
- Connecticut: some gem.
- San Diego County, California: not much gem material
- Minas Gerais, Brazil, also Rio Grande do Norte, Ceara, other localities; Brazil is the world’s major source of fine aquamarine gems.
- Mursinsk mine, Russia: also other localities.
- Madagascar: fine blue gem material, more than 50 specific localities
- Jos, Nigeria: abundant material, some fine color.
- Mt. Surprise, North Queensland, Australia: (small).
- Myanmar and Sri Lanka: aquamarine has been found, not common there.
- Rossing, Namibia: in pegmatites.
- India: at Madras and Kashmir, medium blue color.
Beryl crystals weighing many tons have been found in pegmatites, but these are never of gem quality. Aquamarines and green beryls, however, may be very large and still be gem quality.
- A crystal was found in Marambia, Teofilo Otoni, Brazil, blue-green, an irregular prism 19 inches long and 16 inches across and weighing 110.2 kg. It was transparent end to end. The famous Martha Rocha aquamarine, found in Brazil, weighed 134 pounds and yielded more than 300,000 carats of superb blue gems. An even larger crystal found in 1910 weighed 229 pounds but yielded only 200,000 carats of cut gems.
- British Museum (Natural History) (London England): 67.35 (blue) and 60.90 (greenish); 879 (sea-green, oval).
- American Museum of Natural History (New York): 272, 215, and 160; also 355 (Sri Lanka), 144.5 (Brazil).
- Hyde Park Museum, New York: 1847 carats.
- Smithsonian Institution (Washington, D.C): 1000 (blue-green, fine color, Brazil); 911 (blue, Brazil); 263.5 (blue, USSR); 71.2 (pale blue, Sri Lanka); 66.3 (pale blue-green, Maine); 20.7 (pale blue, Madagascar); 15.3 (blue-green, Idaho); 14.3 (blue, Connecticut).
- Brazilian Aquamarine: bluish green, (also a misnomer for bluish green topaz).
- Madagascar Aquamarine: fine, medium blue.
- Maxixe Beryl: treated beryl with excellent aquamarine blue, known for fading. Also called halbanite.
Consult our gemstone care guide for recommended cleaning methods.
by Donald Clark, CSM IMG