The Wrekin Ruby, a cricket ball-sized gem owned by collapsed Shropshire firm Wrekin Construction, is to be put up for auction, it was revealed today.

The stone, also known as the Gem of Tanzania, was listed in the assets of Wrekin Construction when it went into administration in March with the loss of more than 500 jobs.

Administrators Ernst & Young confirmed the gem, which was sold to Wrekin in exchange for around £11m worth of shares in the company, would be sold by auction house GVA Grimley in a bid to claw back some of the huge sums which are still owed to creditors.

A spokesman for Ernst & Young, said: “Joint administrators of Wrekin Construction Company Limited – Ian Best and Tom Lukic of Ernst & Young – have instructed GVA Grimley to sell the Gem of Tanzania. Offers for the ruby have been invited, with evidence of funding, by December 16, 2009.”

The gemstone is described in the auction literature as “loose hexagonal crystal rough with co-existent green/black crystal matrix on its sides, opaque reddish purple in colour”. It is said to be about 10,700 carats. Some independent valuations have priced it as low as £300,000.

Administrator Ian Best said: “The joint administrators are seeking to maximise realisations from the Gem of Tanzania for the benefit of the creditors. The gem will be widely advertised in specialist publications.”

Wrekin owes more than £40m to more than 1,000 creditors.