Care for a 603-carat diamond to add to your collection? If you move quickly, you may be able to purchase it from its new owner, but be forewarned: it’s likely to cost you well over $20 million.

On October 9, 2006 the massive diamond called the Lesotho Promise, after the African kingdom in which it was found, sold for a mouth-watering $12.36 million at auction at the Antwerp (Belgium) Diamond Center. The diamond was put on the market by Gem Diamond Mining Company and the government of Lesotho, who jointly own the mine in which it was found. The lucky winner of the Promise is the South African Diamond Corporation, owner of the luxury jeweler Graff, which intends to cut the massive stone into a series of smaller stones. Sold separately, those diamonds are expected to fetch more than $20 million.

The Lesotho Promise is about the size of a chicken’s egg and weighs much the same: 603 carats comes out to about 4.25 ounces, or about a quarter of a pound. It’s roughly triangular shaped, with excellent clarity. There’s a lot of value locked into that small bundle, since the Promise is the tenth-largest white diamond on record (and the fifteen largest overall). White diamonds are typically the most desired color, given their depth of sparkle and eye-catching brilliance. It rates a “D” on the diamond color scale — the highest rating a diamond can receive.

A stone the size of the Lesotho Promise could easily produce diamonds enough to adorn hundreds of diamond engagement rings; even by exaggerated celebrity standards, in which a 3-6 carat diamond engagement ring is business as usual, the Promise would account or more than a hundred pieces of diamond jewelry. However, Graff expects to divide it only into several smaller stones, one of which will be a large heart-shaped diamond that’s likely to take a place beside the Hope, Koh-I-Noor and Tiffany Yellow as icons of the diamond world.

The Lesotho Promise isn’t the largest diamond ever found: that place is held by the Cullinan, at a whopping 3,106 carats, followed by the Excelsior at 995. Both those monster stones were found in South Africa, and so, in a way, was the Promise: the tiny (but sovereign) nation of Lesotho is surrounded on all sides by South Africa. The largest diamond found in 13 years, the Promise came to light on August 22, 2006 at the Letseng Diamond Mine, where it was discovered by a woman sorting rocks by hand — the true find of a lifetime. Prior to its discovery, pride of place at Letseng was held by a diamond called the Lesotho Brown, which was found in 1967. At 601 carats, the Lesotho Brown is now the 16th largest diamond on record; however, its color and clarity do not match that of the Promise. In general, brown diamonds (which are actually shades of yellow) are not considered as valuable as white diamonds.

The Letseng mine, which was originally operated by De Beers, has produced numerous massive stones over 100 carats in weight, including one extracted in 1965 that tilted the scales at 527 carats. De Beers ceased operations in 1982. Operations were renewed in the late 1990s by Gem Diamond Mining and the Lesotho government, after new kimberlite resources were discovered at the locality.