Have more than $100 million to blow?

If so, De Beers has a diamond for you: the 273-carat Centenary diamond, the largest modern-cut, flawless polished diamond in the world.De Beers unveiled the heart-shaped jewel in London on Wednesday, with a lot of security and a touch of drama.

The room was darkened, then a curtain opened. A spotlight lighted up an egg-sized diamond, sparkling on a rotating stand and reflecting colored light around the room.

"A truly rare and unique diamond," declared Nicky Oppenheimer, deputy chairman of his family's diamond mining empire, De Beers Consolidated Mines Ltd.

Unique and thus impossible to value, he said, though De Beers has insured it for at least $100 million.

There are only two larger diamonds in the world, and Queen Elizabeth II owns them.

The largest is the 530.2-carat Great Star of Africa in the imperial sceptre, and the 317.4-carat Lesser Star of Africa in the imperial crown. They are kept in the Tower of London, and their value is not known.

Both were cut 86 years ago from one gem, the Cullinan diamond that was 3,106 carat rough. Like the Centenary, it was found in De Beers' Premier mine in South Africa.

The Cullinan diamond was cut before the "brilliant" cut was fully developed in the 1920s. This involves cutting facets to reflect the most possible light.

The Centenary was found in the mid-1980s through the normal mechanized mining process in the mine, Oppenheimer said.

The rough Centenary diamond, which weighed 599 carats, was unveiled at the company's centenary celebrations in South Africa in 1988.

It then took three years to prepare, cut and polish the jewel, Oppenheimer said. The Centenary diamond is more than twice the size of the next largest comparable stone, the company said.

Gabi Tolkowsky, whose great-uncle developed the modern cutting methods, cut the Centenary diamond in a cellar in Johannesburg.

The Centenary was a difficult stone to cut and polish because its shape did not suggest an obvious approach for yielding the jewel locked within, the company said. In its rough form, the diamond resembled an irregular matchbox.