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Gemstones: Aquamarine

Aquamarine Gemstones


Source: Brazil, Kenya, Madagascar, Mozambique, Russia, Tanzania, Uruguay, USA, Zambia

Birthstone: March (alternate: bloodstone, diopside, or green jasper)

The name "aquamarine" (aquamarin German, aqua marina Spanish) is derived from the Latin phrase "water of the sea," named for its greenish-blue seawater color. Aquamarine (or aqua beryl) develops in granite pegmatites and certain types of metamorphic rock. It occurs in conjunction with quartz, microcline, muscovite, and almandine in metamorphic pegmatite. Most aquamarine comes from the pegmatites of Minas Gerais Brazil, where crystals weighing several pounds have been found.

Aquamarine is transparent to translucent member of the beryl family of minerals (emerald, morganite, heliodor), and is a cyclosilicate that is made up of beryllium (Be), aluminium silicate, sodium (Na), lithium (Li), and cesium (Cs). Beryl has become an important source for the element Berillium (Be), a metal with a variety of commercial and military uses, such as in the manufacturing light-weight metal alloys.

Aquamarine Crystal in situ

Aquamarine crystal in situ (Photo: Public Domain)

   Alluvial Aquamarine Crystals

Alluvial (placer) aquamarine crystals

Aquamarine's turquoise-blue color is due to the presence of ferrous iron atoms and the presence of ferric iron causes a yellow tint. A yellow, greenish-yellow or golden beryl from Brazil is sometimes referred to as "aquamarine chrysolite," although the correct name for this variety of beryl is heliodor. Pale greenish-blue sapphire, which is a mineral variety of corundum - not beryl, is sometimes referred to as "Oriental aquamarine."

Aquamarine Crystal System & Crystal Habit

Aquamarine crystal is generally vertically striated or grooved and pleochroism is distinct in deeply colored crystals. Occasionally, some specimens of aquamarine display chatoyancy. Aquamarine has imperfect cleavage which runs parallel to the basal pinacoid.

Aquamarine (Beryl) Crystallography, Chemistry, Physical Properties

Crystal System hexagonal
Crystal Habit prismatic, parallel and elongated
Specific gravity (SG) 2.67 to 2.75
Mohs Hardness Scale 7.5 to 8.0
Toughness good
Fracture conchoidal
Cleavage imperfect
Streak white
Chemical Composition Be3Al3[SiO3]6

Aquamarine (Beryl) Optical Properties

Optical Properties double refractive
Refractive Index 1.565 to 1.580
Birefringence .005 - .009
Pleochroism weak to moderate
Surface Luster vitreous
Diaphaneity transparent, translucent
Gem Color blue, greenish-blue, yellowish-brown, yellowish-green

Santa Maria Aquamarine from Brazil

Perhaps the largest aquamarine ever found was the 552,500 carat Papamel Aquamarine, found in 1910 at the Batadal mine near the village of Ponto de Marambaia, in Minas Gerais, Brazil. One of the larger near-flawless aquamarine crystals ever found was the "Dom Pedro aquamarine" found in 1993 in Minas Gerais, and weighing 10,395 carats (24,875 grams).

Brazil's principal aquamarine region begins about 75 miles north of Rio de Janeiro and includes the areas of ArujŠ, Conselheiro Pena, Governador Valadares, Jequitinhonha River basin, Pedra Azul, Salinas, and Teůfilo Otoni. The town of Teofilo Otoni in Minas Gerais is a major Brazilian gem-trading center known for its aquamarine. Some of the highest quality specimens of brilliant blue "Santa Maria" aquamarine come from the Santa Maria de Itabira Mine. Aquamarine from africa that has the same intense blue color is called "Santa Maria Afrique."

Principal aquamarine mines in the Brazilian state of Minas Gerais are the Batadal Mine, Papamel Mine, Santa Maria de Itabira. Brazilian aquamarine with a paler blue color are referred to as "Esperito Santo" for the state of the same name.

Aquamarine Inclusions

Due to aquamarine's pale color and typically high transparency it is relatively easy to see any inclusions that are present within the stone.

Aquamarine Inclusions

Aquamarine Enhancements

Most Aquamarine on the market today is heat treated to bring out the greenish-blue color that is characteristic of the stone. Yellowish-brown or yellowish-green stones are heated to 400 to 450 degrees Celsius to bring out a deep blue color. The resulting color change of the aquamarine is permanent and the treatment is difficult to detect. Synthetic blue spinel is easy and inexpensive to produce, and is often mistakenly sold as "synthetic aquamarine."

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