The Cullinan is estimated to have formed in Earth’s mantle transition zone at a depth of 410–660km (255–410 miles) and reached the surface 1.18bn years ago. It was approximately 10.1cm (4.0in) long, 6.35cm (2.50in) wide, 5.9cm (2.3in) deep and weighed 3,106 carats (621.2g). It was so three times the size of the Excelsior Diamond, found in 1893 at Jagersfontein Mine, weighing 972 carats (194.4g). Four of its eight surfaces were smooth, indicating that it once had been part of a much larger stone broken up by natural forces. It had a blue-white hue and contained a small pocket of air which at certain angles produced a rainbow.
Shortly after its discovery, the Cullinan went on public display at the Standard Bank in Johannesburg, South Africa, where it was seen by an estimated 8,000–9,000 visitors. In April 1905, the rough gem was deposited with Premier Mining Co.’s London sales agent and sent to the United Kingdom in a plain box via registered post. On arriving in London, it was conveyed to Buckingham Palace for inspection by King Edward VII. Although it drew considerable interest from potential buyers, the Cullinan went unsold for two years. In 1907, the Transvaal Colony government bought the Cullinan for £150,000, which adjusted for pound-sterling inflation is equivalent to more than £16m in 2022. Prime Minister Louis Botha then presented it to Edward VII, King of the United Kingdom, who had it cut by Joseph Asscher & Co in Amsterdam.
The Cullinan produced nine major stones of 1,055.89 carats (211.178g) in total, plus 96 minor brilliants and some unpolished fragments weighing 19.5 carats (3.90g). All but the two largest stones—Cullinans I and II—remained in Amsterdam by arrangement as the fee for Asscher’s services, until the South African government bought them (except the Cullinan VI, which Edward VII had purchased and given to his wife Queen Alexandra in 1907) and the High Commissioner for Southern Africa presented them to Queen Mary on 28 June 1910. Mary also inherited the Cullinan VI from Alexandra and she left all her Cullinan diamonds to her granddaughter Elizabeth II in 1953. The Cullinans I and II are part of the Crown Jewels, which belong to the Queen by right of the Crown.
Asscher sold the minor stones to the South African government, who then distributed them to Queen Mary, Louis Botha, then prime minister of South Africa, the diamond merchants Arthur and Alexander Levy, who supervised the cutting of the Cullinan, and Jacob Romijn who co-founded the first trade union in the diamond industry. Some were set by Mary into a long platinum chain, which Elizabeth has never worn in public, saying that “it gets in the soup”.