When miners unearth the world’s biggest and rarest of diamonds — like the golf-ball-sized, 357-carat rock found this year in the southern African kingdom of Lesotho — figuring out what they are worth can prove almost as difficult.
Gem Diamonds Ltd., which specializes in digging up stones that only a few billionaires are likely to buy, has been taking some unusual steps to confront that dilemma. The London-based mine owner is replicating on a small scale what middlemen normally do.
It cuts, polishes and re-sells some diamonds to get a better sense of what the market is for the world’s biggest ones. In September, the company had its biggest sale ever when its prized discovery from Lesotho fetched $19.3 million.
“There’s no such thing as an accurate valuation on these stones,” Brandon de Bruin, head of sales at Gem Diamonds, said during an interview in Antwerp, the center of the world diamond trade.
Of the hundreds of millions of diamonds unearthed over the past decade, only about a dozen bigger than 250 carats were found, based on a Bloomberg review of company disclosures.They are so rare that miners aren’t always sure they’re making the best deal.
Because large stones favored by the super-rich have held their value during a slump in prices for smaller, more-common ones, producers have an even bigger incentive to get the best price on their big discoveries.
Lucara Diamond Corp., which last month found the second-largest ever, hasn’t yet put a price tag on a 1,111-carat gem the size of a tennis ball, which analysts say could fetch $60 million.
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