17th Conference of the LFG: Colombian Emeralds
On Wednesday 16 May 2018, the French Gemmology Laboratory gave its 17th conference dedicated to Colombian emeralds, in partnership with the French Gemmology Association.
Annabelle Herreweghe, gemmologist at LFG and Aurélien Delaunay, head of the LFG, shared the organisation’s latest news with the audience. In gemmological news, of particular note were the extraordinary etch channels found in one diamond (https://www.gia.edu/gems-gemology/spring-2018-microworld-type-iia-diamond-with-reform-etch-channels), amazonite treated by dyeing and impregnation, opals treated by dyeing, Dumortierite gemstones from Madagascar, fine blowing, etc.
The conference on emeralds was facilitated by Gaston Giuliani, geologist and director of research at IRD and CRPG in Nancy. A specialist in emeralds, he has focused his research since 1985 on this remarkable gem and supplemented his work with numerous study trips to Brazil and Colombia.
Considered the purest and most sought-after variety in jewellery, the first Colombian emeralds developed 65 million years ago in the Andes Mountains.
Emerald is a variety of beryl, which derives its green colour from traces of chromium and vanadium. It is rare and thus precious, its formation requiring exceptional geological conditions: the presence of beryllium, the main component of the beryl, is mainly found in the magma of the earth’s crust, as well as the presence of chromium and vanadium, which are in contrast located in the Earth’s mantle. Such is the paradox of emerald: the three metals that form it, geologically incompatible, uniquely come together in this gemstone. It is truly the result of chance.
In Colombia, exceptional geological conditions came together, making it possible for these extraordinary deposits to be created. Granite, an essential component of the earth’s crust, came into contact with the mantle rocks. A fluid then came along to trigger a chemical reaction and transformed all the rocks, and the conditions for the formation of emeralds.
The largest fields of emeralds are found in Colombia, Brazil, Russia and Zambia. The main Colombian production sites are the Chivor, Muzo, Peñas Blancas and Coscuez Mines. Colombia currently provides for 55% of the world’s emerald production (source 2011).
The particularities of Colombian Emeraudes
Colombian emeralds are found in organic shale, which occurs in the eastern or western Andes Mountains. The formation of emeralds, which took place between 65 million years and 35 million years ago, came with structural deformations to the Cordillera (the Nazca plate colliding with the South American plate). The distinct configuration of the geological layers in this territory enabled the creation of exquisitely beautiful emerald crystals, often large in size, such as the Gachalà emerald. Some crystallographic originalities are particularly sought after by collectors, most notably trapiche or six-branch star emeralds.