Building company Wrekin Construction collapsed in May, another victim of the recession.

Another reason was surely the re-valuing of the company's greatest asset: a 2.1kg ruby, the Gem of Tanzania, thought to be worth £11m.

The stone may well be 2.1kg, but it certainly isn't worth £11m. The "ruby" was revealed to be mostly anyolite, a low-grade mix of ruby and other substances.

The fake stone was first bought in 2002 by a South African businessman for £13,000, and later re-valued at £300,000. It was most recently picked up by Wrekin's owner, David Unwin in 2007, as part of a land deal.

In recession-hit 2009, the "ruby" was key to propping up the company's fortunes until six months ago, when the company went bust and 500 jobs were lost.

Ordinarily, a real 2kg perfect ruby would be worth a vast amount. A 2kg lump of anyolite, however, is unlikely to bring more than £100.

Ernst and Young have advertised the "gem" in Britain's Rock 'n' Gem magazine and America's Colored Stone Magazine. But it will be unlikely to make the month's top sale, unless for the story associated with it.

The story is a dire warning to gem collectors and investors: always be sure to check the credentials of any gems or jewellery that you are considering buying.

Also, make sure that the seller is reliable. For instance, documents related to the most recent sale of Wrekin's "Gem of Tanzania" were found to be forged.

And don't be dazzled by value. In this case, the £11m price tag could have distracted potential buyers from making the necessary authenticity checks.

Wrekin aren't the first organisation to have been duped recently. Back in August, a Dutch Museum was brought back down to Earth when it a emerged that a prized pieced of moonrock was fake.

____________________________________________________________