A white diamond nearly the size of an egg sold for 21.6 million Swiss francs ($21.75 million; € 20.63 million), including fees, at a Christie's auction on Wednesday.

The auction house said the diamond, dubbed "The Rock," was one of a kind and the price it fetched was on the lower end of the expended auction range.

Christie's pre-sale estimate said the pear-shaped diamond could go for between $19.1 million and $30.1 million.

Diamonds can be of many colors, ranging from D, which is colorless, to Z, which is visibly yellow.

"The Rock" was G-color, which is among the top grades in the range of diamonds that are nearly colorless. Diamonds that are absolutely colorless cost even more.

'Unchartered territory'

The 228-carat diamond, with its platinum pendant mounting, has a gross weight of 61.3 grams (2.2 ounces).

It has dimensions of 5.4 centimeters by 3.1 centimeters (2.1 inches by 1.2 inches).

Max Fawcett, head of jewelry at Christie's in Geneva, hailed a successful sale in "uncharted territory" for a stone of its kind.

'Red Cross' diamond fetches over $14 million

Christie's also sold a 205-carat yellow diamond for $14.28 million on Wednesday.

The diamond, cut from a rough stone unearthed in South Africa's Griqualand mines in the early 20th century, sold for double the pre-sale estimate.

The diamond first went up for auction in 1918, with Fawcett saying there was a "huge amount of interest" for it this time around.

Fawcett also said that an unspecified seven-figure sum from the proceeds of the sale would be donated to the Geneva-based International Red Cross.

AFP material contributed to this report