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Fake Stone Alert #1 Rare Bi-Colour Natural Corundum

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This is an Ebay story.

The Victorian Division recently – and on purpose – purchased a couple of “rare bi-colour natural Corundum” of Ebay for the teaching collection. The stones were all green, and peppered with blue dots. The stones were sold with certificates stating “Natural Sapphire”. The stones cost less than $10 per piece, with free postage.

The material – from the Ebay listing – was immediately recognisable as synthetic Corundum produced by the Verneuil method, and was interesting for the large number of obvious gas bubbles with concentration of blue colour.

According to Richard Hughes in Ruby and Sapphire – a Gemmologist’s Guide, gas bubbles occur in layers within the boule which follow the curved growth lines. Some of the specimens purchased from Ebay indeed show layers of gas bubbles distinctly following curved growth lines.

It is common for synthetic blue Corundum to show colour concentration around gas bubbles, however, I have not seen green corundum displaying the same. Given the large number of these stones available on Ebay at the time of purchase – and from a number of different sellers, it appears this material may have been manufactured deliberately to attempt to mimic a bi-colour gemstone.

Interestingly, I purchased a partial half boule from a Russian manufacturing firm just 12 months earlier that was also green. A portion of the surface of the boule is coloured blue, and a large number of gas bubbles are present, some with blue colour concentration. At the time I thought it was an interesting specimen that displayed the classic elongated gas bubbles, which typically form at right angles to the curved growth lines and near the top of the boule.

For those of us who are trained Gemmologists, the above story may elicit a laugh, however, the audience on Ebay are often not trained Gemmologists, and certificates are usually the currency to ensure trust in the transaction. Trust that the stone is correctly identified and advertised. However, not all certificates are legit.

No doubt some of these stones may make their way onto Australian shores, and be brought into jewellery stores by unsuspecting members of the public to be made up into jewellery.

Laura Brehaut FGAA Dip DT is a qualified gemmologist and the current GAA Victoria President.

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