How the world’s largest diamond came to be part of the UK's Crown Jewels

By Sanj Atwal
split image of largest diamond and Queen Mary

The largest diamond ever found was unearthed over a century ago, on 26 January 1905 at the Premier Mine near Pretoria, South Africa.

Named after the mine’s owner, Thomas Cullinan, the rough diamond weighed 3,106.75 carats (621.35 g; 1.37 lb) and measured 10.5 cm (4.1 in) at its longest point.

The Cullinan Diamond was three times larger than the previous record holder, the Excelsior Diamond, found in 1893 at another South African mine.

Uncovered 5.5 metres (18 ft) underground, the Cullinan is estimated to have been formed at a depth of 410–660 km (255–410 miles), reaching the Earth’s surface 1.18 billion years ago.

The Cullinan Diamond

After its discovery, it was briefly put on public display at the Standard Bank in Johannesburg, where up to 9,000 people came to see it.

In April of the same year, Premier Mining Co. sent the Cullinan to London to be sold.

News circulated of the diamond being transported on a steamboat, where it was locked in the captain’s safe and protected by detectives. However, this was all a diversionary tactic to mislead potential robbers; the real Cullinan was simply posted to England in a plain box. 

When it arrived in London, the Cullinan was taken to Buckingham Palace and viewed by King Edward VII before being put up for sale.

Despite attracting much interest, it remained unsold for two years until 1907, when the Transvaal Colony government bought it for £150,000, which is equivalent to £14.9 million ($18.1 m) adjusted for inflation in 2023.

The Transvaal Colony was the name given to South Africa’s Transvaal region under direct British Rule after the Second Boer War. Its Prime Minister, Louis Botha, proposed purchasing the Cullinan as a gift for King Edward VII to demonstrate the region’s loyalty to the British monarchy.

Sir Richard Solomon, Agent-general of the colony, presented the Cullinan to the king at his 66th birthday party, witnessed by many high-profile guests such as the queens of Spain and Sweden.

King Edward VII later announced, via his colonial secretary Lord Elgin, that he’d accepted the “great and unique” diamond to preserve it “among the historic jewels which form the heirlooms of the Crown".

The nine major stones cut from the rough Cullinan diamond

The Cullinan was then sent to Amsterdam to be cut and polished by Joseph Asscher & Co. Three workers took eight months to cut the rough stone into nine major stones and 96 minor brilliants.

The largest one, Cullinan I, was nicknamed the “Great Star of Africa” by the king, and the second-largest, Cullinan II, was dubbed the “Second Star of Africa”. Both became part of the UK’s Crown Jewels.

Weighing 530.2 carats (106 g; 3.7 oz), Cullinan I is the world’s largest clear cut diamond. It sits at the top of the Sovereign’s Sceptre with Cross, the ornamental rod held by the British monarch at their coronation.

Cullinan II is mounted in the Imperial State Crown, which is worn by the monarch at the annual State Opening of Parliament.

Portrait of Queen Mary wearing Cullinan I and II as a brooch on her chest, III as a pendant on the Coronation Necklace, and IV in the base of her crown, below the Koh-i-Noor

The seven other major diamonds, in addition to several minor brilliants and unpolished fragments, went into the possession of Queen Mary, daughter-in-law of King Edward VII and wife of King-Emperor George V.

After her death, they were inherited by Queen Elizabeth II, who was said to refer to the smaller ones as “Granny’s rocks”.

The inheritors of Queen Elizabeth II’s private jewel collection have not been confirmed, but it is thought that much of it has gone to Queen Consort Camilla and the Princess of Wales.

Cullinan I and II remain part of the Crown Jewels, currently in the custody of King Charles III.

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