Aquamarine - Encyclopedia

    Class : Silicate
    Subclass : Cyclosilicate
    Crystal system : Hexagonal
    Chemistry : Be3Al2Si6O18
    Rarity : Common

Aquamarine is a transparent to translucent variety of beryl from pegmatites. Its blue-green to blue color is due to iron that it contains in trace. Its name comes from the Latin aqua (water) and marina (marine) because of its color reminds the ocean. It is a mineral known since Antiquity. Aquamarine crystallizes in elongated prisms with hexagonal sections, sometimes bevelled often with flat terminations. It is a mineral variety with a strong importance for jewelery. It is extremely appreciated and used despite of a relative fragility.

Aquamarine in the World

Aquamarine is present in many occurrences around the world, it is impossible to mention them all. The largest crystals were extracted from the pegmatites of Minas Gerais in Brazil (Galileia, Coronel Murta, Teofilo Otoni, Virgem da Lapa, etc...). These deposits produced gemmy crystals usually exceeding 15 cm. At the end of the 80's a crystal of 91 cm was discovered for a total mass of 45 kg, it was cut in 1992-1993 by Bernd Munsteiner in an obelisk of a total mass of 10 363 carats (more than 2 kg ), for a finished size of 36 cm by 10 cm. This jewel was donated to the Smithsonian Institution by Jane Mitchell and Jeffery Bland and is now called "Dom Pedro" in tribute to two Brazilian emperors, it is the largest aquamarine gemstone in the World (photo on the right). The Pakistani pegmatites also produce very fine pale blue decimetric groups, commonly associated with black tourmaline, albite and quartz. The pegmatites of the Erongo region of Namibia have also produced groups of fairly colored crystals on orthoclase with sometimes even green fluorite (photo from the top of the page). Different sites in Russia (Nerchintsk, Siberia), Madagascar and Zimbabwe have also provided magnificent crystallizations. The Chinese pegmatites of Xuebaoding Mount (Pingwu) currently produce the most aquamarines, this deposit has become in some years the leading producer of aquamarine in the world for jewelry, the crystals are small and very light in color. Finally, it is necessary to emphasize the new Vietnamese deposits which currently produce very colored crystals sometimes of more than 10 cm with superb terminations.

Amazing aquamarine crystal on quartz from Pakistani pegmatites

Fantastic blue aquamarine from Vietnam

Gemmy aquamarine and quartz from Vietnam

4,03 ct aquamarine in fancy cut

Aquamarine in France

In France aquamarine is present in some pegmatites of Limousin : crystals of 5 cm have been reported in Chanteloube Haute-Vienne.

Note also the huge stony but bluish Beryl pegmatites of Biauchaud at St-Pierre la Bourlhonne in Puy-de-Dome (photo on the left), where aquamarine is associated with 
schorl in a massive quartz.

We also find aquamarine more anecdotally in micro-crystals in the La Lauzière Massif, in French Alps.

Twinning and special characteristics

Beryls and especially aquamarine never present twinning but some inclusions can be spectacular. We note especially a series of fluid or gaseous inclusions called "helicoidal" or "spiral" inclusions propagating on the axis of elongation of the crystal (photo right). These characteristic inclusions of beryls are due to rapid growth by "screw dislocation" along the axis of elongation.

Fakes and treatments

Among the classic scams, there are assemblages of broken crystals stuck on pieces of pegmatite (left picture). The collage is usually hide with crushed muscovite and not necessarily visible at first glance. Note that these fake are generally made in Pakistan with the material collected in this region, so it is not uncommon to find unlikely parageneses : aquamarine, topaz, pink fluorite, morganite, apatite, etc...

Because of the importance of aquamarine in jewelry, it is a gemstone that is widely treated. Indeed in nature, the crystals are generally near colorless. To remedy this "problem", aquamarine is very largely heated to improve the color, this treatment is impossible to detect without advanced laboratory equipment. Generally in the market, gemstones with a bright color without inclusion are usually all treated.

Finally in the same way like emerald, aquamarine can be synthesized in laboratory, characteristic chevrons inclusions, visible under magnification, but only an expert eye can locate them. Further investigations based on the isotopy of oxygen allow to make the difference.

Hardness : 7,5 to 8
Density : 2,68 to 2,91
Fracture : Conchoidale to uneven
Trace : White

TP : Transparent to opaque
RI : 1,564 to 1,593
Birefringence :  0,004 to 0,007
Optical character : Uniaxial -
Pleochroism : Weak
Fluorescence : None

Solubility : Hydrofluoric acid

Magnetism : None
Radioactivity : None