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Gemstones

Articles from GEMSTONES - AMBER (4 Articles)











Organic Gems Part I: Amber

Organic gems are a group of relatively rare and decorative materials that have an animal or plant origin. Amber is fossilised tree resin prized for its rich golden hues. When plant or animal fragments are suspended within the material, they can offer a fascinating peek into our planet’s primordial past.

Amber is one of the more well-known organic gems, commonly ranging in age between 1–300 million years old. Chemically, amber is a hydrocarbon – a compound of carbon, oxygen and hydrogen – although the chemical constituents vary between sources worldwide. Unearthed predominantly in the Baltic Sea region of Europe, it is also found in the Dominican Republic, Myanmar, Mexico and some other European localities.

As a defence against injury, disease and/or insect and fungal attack, a tree may exude resin. Initially a soft, sticky substance, the resin may engulf bits of bark, insects, small creatures or parts of plants, as it slowly oozes out from resin canals within the tree.

Not all tree resin is destined to become amber. Much like all fossils, there are specific environmental conditions of heat, pressure and biology that are required for the fossilisation to take place. The two-part process of transformation from tree resin to amber is called ‘amberisation’.

"Not all tree resin is destined to become amber – like all fossils, there are specific environmental conditions of heat, pressure and biology that are required for the fossilisation to take place"

Over the course of 2–10 million years, the resin begins to harden through a process of molecular polymerisation. Here, the resin must be in an anaerobic (oxygen-free) condition under layers of overlying sediment, where pressure and heat can transform the soft resin into harder and more stable ‘copal’ resin.

From here, sustained heat and pressure can further evaporate terpenes (organic compounds within the resin) to form a hard, solid natural plastic – amber. Evidence suggests that Baltic and Dominican amber were created in a very specific anaerobic environment – extended immersion under seawater.

Amber ranges from colourless to yellow, brown, red, black, green, and very rarely blue. The colour of some Dominican amber shows a bluish fluorescence in daylight, appearing to alter the otherwise brownish hue.

While amber may be transparent through to opaque, transparent material is typically the most sought after. The darker, reddish material is more valuable, but inclusions play a huge part in the final value. Pieces that contain plant or animal inclusions will fetch a much higher price than those that are completely free of inclusions.

Man-made plastics, glass and composites are commonly used to imitate amber, and occasionally a high-quality imitation – with insects implanted – will fool most people.

Opaque amber contains tiny gas bubble inclusions that give it a cloudy appearance. Natural oxidation can darken amber over time, but colour and clarity can be improved by heat treatment and dyeing.

A common treatment involves careful heating in canola oil to infill the cavities and improve clarity. Slow cooling is imperative to minimise the occurrence of circular stress fractures, described as ‘sun spangles’. These delicate inclusions are evidence that this clarification process has taken place.

Like all gemstones, there is a story behind amber’s beauty, and it tells a compelling tale of prehistoric Earth.











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

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Sunday, 20 October, 2019 06:39pm
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