International Gem Society

Donald Clark, CSM founded the International Gem Society (IGS) in 1998. IGS’s mission is to make gemology information accessible and affordable to everyone. IGS has members on every continent (except Antarctica), who range from seasoned professionals to hobbyists. IGS offers members multiple resources, including a reference library that is updated weekly and gemology certification courses.

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Most expensive emerald per carat

The 18.04-carat Rockefeller Emerald, set within a platinum and diamond ring, achieved $5,511,500 (£4,316,250; €4,927,450) – including buyer's premium – at Christie's auction house in New York City, USA, on 20 June 2017. The gem was purchased by the American jewellery firm Harry Winston. This represents a per-carat price of $305,515 (£239,259; €273,140).