Keeping giant gems intact during mining a challenge for producers

London

A BLACK-AND-YELLOW dump truck rumbles up from a giant pit in the mountains of southern Africa, carrying a load of freshly blasted slate-grey rock from the Letseng mine. With luck it will contain a golf-ball sized diamond worth perhaps US$20 million. With even more luck the stone won't get smashed.

Keeping giant gems intact during the mining process is a challenge for the two companies that account for most of the global production of these multimillion-dollar whoppers. They've unearthed 15 of the 20 largest diamonds found in the past decade. Almost every one lost a chunk at some point in the process, including a stone called the Lesedi La Rona that is the largest found in more than a century.