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Image courtesy: Greg C Grace
Image courtesy: Greg C Grace

Colour Investigation: Beryl

The beryl family includes some of the world’s most loved gemstones. STACEY LIM reports that varieties of beryl are prized for their hardness, transparency and range of beautiful colours.

From the peachy pinks of morganite to the rich greens of emerald, beryl’s dramatic colour variations are due to trace elements in the environment in which they crystallise.

Beryl is an allochromatic mineral that owes its colour to trace impurities rather than its own constituent elements. Goshenite is colourless beryl and the most chemically-pure form of beryl. Other varieties are coloured by different impurities in the crystal structure. These trace impurities resonate in light and absorb specific parts of the spectrum. The remaining light transmitted or reflected to the eye gives colour to the gemstone.

Beryl’s most well-known and valuable variety is emerald, presenting green to bluish-green gemstones, not to be confused with green beryl. To be classified as emerald, the green colour must be the result of the presence
of chromium and/or vanadium replacing aluminium in the crystal lattice. Fine-quality emerald presents as an almost unmistakable and vivid velvety green. It is one of the few gemstones where visible inclusions are actually acceptable.

In contrast, green beryl is yellowy-green to deeper green. It is coloured by ferric iron and never produces a vivid enough green to rival emerald. Also coloured by iron is heliodor, a pale yellow to rich golden yellow variety of beryl.

Aquamarine owes its delicate blue-green palette to ferrous iron. Loved for its icy sky-blues and cool sea greens, its name originated from the Latin aqua marina, meaning ‘water of the sea’. Available in large, eye-clean gemstones, aquamarine’s
colour and higher carat weights has made it popular, although deeper shades command a higher price. Most commercially-available aquamarines are heat-treated to remove yellowy tones and produce a more desirable blue hue.

Maxixe beryl is the name given to blue beryl with a very dark tone that is almost unnatural, unlike the softer blues of aquamarine. The colour is known to fade from deep blue to a yellowish tone in sunlight and strong artificial light or heat in a reasonably short time. The maxixe beryl’s colour is caused by a nitrate trace compound. Some maxixe-type beryl is also on the market with colour resulting from a carbonate trace compound.

Morganite’s colour range includes pink, purple-pink and orange-pink, and the gemstone owes its pretty hues to manganese. In today’s market, the rosier tints are more favoured and gemstones are heat-treated to drive off the yellow or orange tinge, leaving a more pure and attractive pink. Gemstones are generally eye-clean and cut into a variety of shapes and carat weights, and those gemstones presenting strong colour saturation are the most rare and valuable.

Red beryl has a purplish red to deep-red colour caused by the presence of manganese and caesium oxides but it is rare and not as commercially available as the other beryl varieties.

It can be a challenge to select the perfect beryl; however, find one with an unusual hue and consumers will be sure to enjoy a more unique gemstone than they ever thought possible.












ABOUT THE AUTHOR
Stacey Lim

Contributor • Registered GAA Gemmologist & Valuer


Stacey Lim FGAA BA Design, is a qualified gemmologist and gemmology teacher/assistant. She is a jewellery designer, marketing manager and passionate communicator on gemmology. For information on gemstones, visit: gem.org.au









Monday, 16 July, 2018 08:25pm
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