The Rock, the biggest white diamond ever auctioned, sold for 21.7 million Swiss francs ($21.9 million) on Wednesday, far short of the record for such a jewel.

The 228.31-carat stone, larger than a golf ball, was sold in Geneva by Christie's auction house.

There had been high hopes that The Rock would smash the world record for a white diamond, which stands at $33.7 million, a sum fetched in Geneva in 2017 for a 163.41-carat gem.

But the bidding, which started at 14 million Swiss francs, ground to a halt after two minutes at 18.6 million, with the price rising to 21.7 million once the buyer's premium was added on.

The pre-sale estimate had been 19-30 million Swiss francs.

The Rock, a perfectly symmetrical pear-shaped diamond, was sold by an unnamed owner from North America. It was bought by a private collector bidding by telephone.

'The Rock' white diamond could fetch $20-30 million -- or more
'The Rock' white diamond could fetch $20-30 million -- or more AFP / Fabrice COFFRINI

Rahul Kadakia, Christie's international head of jewellery, brought down the hammer to applause in the sale room in the plush Hotel des Bergues.

Diamonds are graded in colour from D to Z and Kadakia told AFP that despite falling short of the overall record, The Rock had set a new world record price per carat for a G-colour diamond.

"When you look at the price per carat -- 100,000 per carat -- this is the level of a D colour diamond, and we achieved that for a G colour diamond. So in fact, we're very pleased as are the sellers, as is the buyer."

Max Fawcett, head of the jewels department at Christie's auction house in Geneva, said there were only a handful of diamonds of similar size and quality to The Rock.

The large diamond was extracted from a mine in South Africa in the early 2000s and has been shown in Dubai, Taipei and New York ahead of the sale in Geneva.

The 'Red Cross Diamond' is among the largest diamonds in the world and bears the shape of a Maltese cross
The 'Red Cross Diamond' is among the largest diamonds in the world and bears the shape of a Maltese cross AFP / Fabrice COFFRINI

The Rock was up for grabs alongside a historic intense yellow diamond associated for more than a century with the Red Cross.

A seven-figure chunk of the proceeds will be donated to the International Committee of the Red Cross, headquartered in Geneva, at a time when war is once again stalking the European continent.

The Red Cross Diamond, a cushion-shaped, 205.07-carat canary yellow jewel, sold for 14.2 million Swiss francs including the buyer's premium -- well above its price estimate of seven to 10 million francs.

Multiple bidders fought fiercely over the gem for 10 minutes, ending in a duel in increments of 50,000 francs before one private collector won through.

The original rough stone was found in 1901 in a De Beers company mine in South Africa and is said to have weighed around 375 carats.

As well as ranking among the largest diamonds in the world, a striking feature is its pavilion, which naturally bears the shape of a Maltese cross.

The stone was first put up for sale on April 10, 1918 at Christie's in London. It was offered by the Diamond Syndicate in aid of the British Red Cross Society and the Order of St John.

The Red Cross Diamond fetched ?10,000 -- approximately ?600,000 ($740,000) in today's money. It was bought by the London jewellers S.J. Phillips.

It was sold again by Christie's in Geneva in 1973, fetching 1.8 million Swiss francs, before being offered by the auction house for a third time.

"A 104-year history of the diamond with Christie's; we're very pleased that we were able to locate it, and we're very pleased that we were able to secure it in another private collection," said Kadakia.

It was estimated at 400,000 to 600,000 Swiss francs. However, it sold for way more: 2.4 million francs, having caught the eye in a prominent spot at the pre-sale exhibition.