US court to solve mystery of the giant £255m gem

The world's most valuable and misshapen piece of rock is set to be Exhibit A in what promises to be one of the most convoluted cases in the history of the Californian court system. It might not amount to much were it not for the fact that the boulder is an emerald worth $400m – some £255m.

At issue is the ownership of what is known as the Bahia Emerald. A Californian, Anthony Thomas, claims he bought the emerald from a Brazilian gem dealer for $60,000 shortly after it was dug up in Bahia in 2001. Mr Thomas arranged for the emerald to be shipped to his home in the US, but it never arrived. He said he was tricked by the dealer into believing the emerald had been stolen, so that it could be sold to someone else for a higher price.

Exactly what happened after that remains a mystery, though it is believed the emerald was stored in a New Orleans warehouse that was flooded during Hurricane Katrina, and also appeared in Idaho. Police recovered the emerald in Las Vegas in 2008 after it was reported stolen from a Los Angeles warehouse. One of at least five claimants to the stone is a man who says he was employed by the Brazilian owners to sell it. Another is Todd Armstrong, who claims he received the emerald as collateral from a gem dealer after a shipment of diamonds he paid for was never delivered. Mr Armstrong was trying to sell the rock when police seized it in Las Vegas.

The emerald will remain in the possession of the authorities until an owner is decided by the court in a trial that begins on 8 September.