Egg-sized diamond called The Rock fetches £17.7m at Swiss sale

An egg-sized white diamond billed as the largest of its kind to go up for auction has sold for more than 21.6 million Swiss francs (£17.7 million) including fees.

The 228-carat pear-shaped G-Colour stone known as The Rock – with its platinum pendant mounting – has a gross weight of 2.2oz and dimensions of 2.1in by 1.2in, making it about the size of a medium hen’s egg.

G-Colour is not the highest grade, but fourth on the letter rung below the top-grade D-Colour diamonds.

An unspecified private buyer acquired The Rock at the low end of the expected range, Christie’s said. The pre-auction estimate was between 19 million and 30 million francs (£15.6 million to £24.6 million).

Max Fawcett, head of jewellery at Christie’s Geneva, hailed a successful sale in “uncharted territory” for a stone of its kind.

Also going under the hammer on Wednesday was the Red Cross diamond, a 205.1-carat fancy yellow stone, which fetched nearly 14.2 million francs (£11.6 million), double the pre-sale estimate.

The diamond was cut from a rough stone unearthed at South Africa’s Griqualand mines in the early 20th century, and went up for auction for the first time in 1918.

Mr Fawcett said there was a “huge amount of interest” in the Red Cross diamond, adding that an unspecified “seven-figure sum” from the proceeds of the sale to an unspecified private buyer would be donated to the International Red Cross Movement, the Geneva-based humanitarian aid group.