The Centenary Diamond, which was discovered at the Premier Mine in South Africa in 1986, was 599 carats (almost 1/3 of a pound!) and was considered internally and externally flawless with its rating of color grade D, the highest grade of colorless diamond.
This diamond was to be cut into a smaller stone; however, the cutting of such an immense and valuable diamond was a significant process. Once an expert was selected to lead a team of diamond cutters, a group of engineers, electricians, and security guards were specially picked to assist in the process. Thirteen different potential designs were presented to the diamond company that owned the Centenary diamond, with a strong recommendation for what would become the eventual modified heart-shaped design.
The final cutting of the Centenary diamond was completed in February of 1991, five years after its discovery, and the diamond was then insured for $100 million USD.
Also take a look at some other Famous Diamonds:
The Hope Diamond
The Cullinan Diamond
The Regent Diamond
The Koh-I-Nur Diamond
The Orlov Diamond