The Cullinan Diamond Was The Largest Diamond In The World

The Cullinan Diamond largest diamond in the world was the largest gem-quality rough diamond ever found,[2] weighing 3,106.75 carats (621.35 g), discovered at the Premier No.2 mine in Cullinan, South Africa, on 26 January 1905. It was named after Thomas Cullinan, the mine's chairman. In April 1905, it was put on sale in London, but despite considerable interest, it was still unsold after two years. In 1907, the Transvaal Colony government bought the Cullinan and then presented it to Edward VII, King of the United Kingdom, who had it cut by Asscher Brothers in Amsterdam.

Cullinan produced stones of various cuts and sizes, the largest of which is named Cullinan I or the Great Star of Africa, and at 530.4 carats (106.08 g) it is the largest clear cut diamond in the world. The stone is mounted in the head of the Sovereign's Sceptre with Cross. The second-largest is Cullinan II or the Second Star of Africa, weighing 317.4 carats (63.48 g), mounted in the Imperial State Crown. Both are part of the Crown Jewels. Seven other major diamonds, weighing a total of 208.29 carats (41.66 g), are privately owned by Elizabeth II, who inherited them from her grandmother, Queen Mary, in 1953. 

The Queen also owns minor brilliants and a set of unpolished fragments.The Cullinan is estimated to have formed in Earth's mantle transition zone at a depth of 410–660 km (255–410 miles) and reached the surface 1.18 billion years ago. It was found 18 feet (5.5 m) below the surface at Premier Mine in Cullinan, Transvaal Colony, by Frederick Wells, surface manager at the mine, on 26 January 1905. It was approximately 10.1 centimetres (4.0 in) long, 6.35 centimetres (2.50 in) wide, 5.9 centimetres (2.3 in) deep, and weighed 3,106 carats (621.2 grams). Newspapers called it the "Cullinan Diamond", a reference to Sir Thomas Cullinan, who opened the mine in 1902. It was three times the size of the Excelsior Diamond, found in 1893 at Jagersfontein Mine, weighing 972 carats (194.4 g). 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, or Newton's rings.

Shortly after its discovery, Cullinan went on public display at the Standard Bank in Johannesburg, 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, S. Neumann & Co. Due to its immense value, detectives were assigned to a steamboat that was rumoured to be carrying the stone, and a parcel was ceremoniously locked in the captain's safe and guarded on the entire journey. It was a diversionary tactic – the stone on that ship was fake, meant to attract those who would be interested in stealing it. Cullinan was 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, Cullinan went unsold for two years.