Huge South African diamond auctioned by Sotheby's

A huge South African diamond estimated at more than $7 million is being sold at auction this Tuesday in Geneva.

This is a Fancy Vivid yellow diamond brooch from Cartier; it weighs more than 100 carats, and it is known as the Allnatt diamond.

"I am holding here the wonderful Allnatt diamond set by Cartier in 1952. We call it Allnatt because the first known owner of the stone was Major Alfred Ernest Allnatt, a British sportsman, collector of old master paintings and philanthropist. He brought this stone to Cartier in 1952, where they created this magnificent flower-inspired setting," explains Catharine Becket, head of sales of magnificent jewelry at Sotheby's, the stone in the palm of her hand.

The 101-carat stone is being sold at auction by Sotheby's, which estimates its value between $6.1 and $7.1 million. It would have been extracted in South Africa more than 100 years ago. And this diamond put on sale for the first time in almost 30 years.

Its importance is such that it has been the subject of international exhibitions, notably at the Smithsonian Museum in Washington DC.

"The stone itself weighs 101.29 carats, it is bright yellow in color, the highest color, and it is BS-2 clarity, i.e. high purity. What is Particularly notable about this stone is the high crown, as you can see here, it's an older style of cutting," says Becket.

The Allnatt is not the only high-value jewel up for sale at Sotheby's Magnificent Jewels and Noble Jewels sale.

An E color diamond, without internal defects, weighing 37.61 carats is expected to sell for between CHF 1,460,000 and CHF 2,370,000 ($1.6M - $2.6M).

In total, there are about 120 lots, many of which have six- or seven-figure estimates.

The auction takes place this May 14 at the Mandarin Oriental hotel in Geneva.