Aquamarine is blue green gemstone cut in variety of shapes. Cabochon, Fancy and Emerald step-cut are popular among the gem cutters, who cater to the demand of the art galleries and collectors from across the world. But are Aquamarines worth the attention they get in the gem market?
Here is how you can find and authenticate a genuine Aquamarine and stay clear from disputes.
1. Heat treatment for colour enhancement
Aquamarine gemstones are heat treated to enhance the colours and impress the consistency. Many untreated aquamarines are also available in the market, but they exhibit translucency and opacity to a certain degree. High quality Aquamarine gemstones are identified by their lighter shades, which means they may not have been heat treated. The stones heat treated to 450 degrees centigrade are often found to have darker shades, but may not be a high quality beryl.
Note: Aquamarines heated beyond a specific high temperature lead to irreversible discolouration. Thus the spectrum of authenticity is very small as far as gems heat treatment range is concerned.
2. Is an aquamarine only blue in colour?
Aquamarines fall in the category of clear blue and clear green beryl family. The coloured Aquamarine and Chrysoberyl resemble very closely to each other. The colourless variety is called Goshenite, but is now tagged as colourless beryl.
3. Specific Gravity is higher than other stones
Aquamarines are heavier than other gems. The stones extracted from Latin American mines have a specific gravity ranging between 2.66 and 2.80. The ones mined from Asia and African mines have higher density due to greater presence of alkali ions.
Gems are immersed in liquids with higher density and the results are noted. Whether the gemstone floats or sinks into the liquid decides the authenticity of Aquamarine.
4. Refractive indices
Aquamarines beads have a refractive index ranging between 1.572 and 1.590. It exhibits a brilliant and unhindered impression when exposed to white light.The originality of the stone is established by placing it under Refractometer. Here are different optical phenomena observed in the real Aquamarine.
Aquamarines can exhibit colour dichroism owing to the presence of more than one colouring ions like chromium, iron and copper. The strength of the colour depends on the percentage of the ions. Birefringence can range between 0.005 and 0.008, which represents the saturation of the colour.
Conchoidal fracture in Aquamarine can cause rainbow effect. It is caused due to diffraction combined with interference.
The Cat’s Eye effect
Aquamarine exhibits chatoyancy due to the presence of rutile in the crystal structure. Rutile is composed of titanium dioxide and can be found in traces in gemstone families like quartz, beryl, chrysoberyl, charoite, tourmaline, feldspar, Labradorite, moonstone, apatite and tourmaline.
Asterism in Aquamarines is a rare phenomenon, but not an exception. Polished, untreated Aquamarines from Brazil show 4-ray star patterns sparingly.
There are different closely linked beryl gems that can be confused with Aquamarine. Study the colour and the crystal lattice under a microscope for further verification.