Rare coloured diamonds to go under the hammer in Geneva

Two rare coloured diamonds are going under the auction hammer in Geneva, with one standout blue diamond discovered in a South African mine last year expected to fetch up to $55m (€51m), which would set a world record for any gemstone.

Today, Christie’s starts off the two-day blitz of jewellery sales with an auction headlined by ‘The Pink’, a 16.08-carat diamond billed as rare for pure colour. Its estimated pre-sale price is between €21m-€26m.

Sotheby’s expects to fetch up to €51m tomorrow with the sale of the 12.03-carat Blue Moon Diamond, said to be among the largest known fancy vivid blue diamonds.

The rare blue diamonds are formed when boron is mixed with carbon when the gem is created.

At that top price, the Blue Moon, so-called in reference to its rarity, playing off the expression ‘once in a blue moon’, would eclipse the record for a diamond at auction: The Graff Pink sold for $46,158,674 at Sotheby’s Geneva five years ago.

The polished blue gem was cut from a 29.6-carat diamond discovered last year in South Africa’s Cullinan mine, which also yielded the 530-carat Star of Africa blue diamond that’s part of the British crown jewels and the Smithsonian Institution’s ‘Blue Heart’, discovered in 1908.

The diamond market could use a boost.

Spokeswoman Margaux Donckier of the Antwerp World Diamond Centre said slower economic growth in China and elsewhere has softened the overall diamond market, but auctions of rare quality pieces was likely to defy market forces.