Aquamarine is the blue variety of the beryl family. Its name means sea-water. In the 19th century, the preferred color for aquamarine was sea-green. Today, the most valued colors are sky-blue and dark blue. Aquamarine is dichroic, appearing blue or colorless as the stone is viewed from different angles.
Gem-quality aquamarine is found as hexagonal crystals, which may be up to 1mm (39in) long and flawless. It has striations along the length of the crystal. Aquamarine stone is often cut with the table facet parallel to the length of the crystal in order to emphasize the deepest coloration.
Some cabochons display a cat’s eye effect due to a fibrous habit. On the other hand, some untreated gems have a greenish tinge.
Occurrence
The best gem-quality aquamarine is found in Brazil. There, it occurs in pegmatites and alluvial deposits of gravels, locally called cascalho. Other localities include Pakistan, Afghanistan, India, Nigeria, and Ural (Russia). A dark blue variety also exists in Nigeria.
Aquamarine Heat Treatment
Almost all aquamarine stone in the market has been heat-treated to enhance its color. Care must be taken not to overheat the stones, as they may become colorless.
Aquamarine Properties
- Specific Gravity: 2.69
- Refractive Index: 1.57-1.58
- Birefringence (DR): 0.006
- Luster: Vitreous
- Crystal Structure: Hexagonal
- Composition: Beryllium aluminum silicate
- Hardness: 7½
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