On January 26, 1905, surface manager Frederick Wells pried a 3,106 carat crystal out of a mine wall in South Africa with his pocket knife, just 18 feet below the surface. The Cullinan was three times the size of the previous record holder, the Excelsior, and it had formed hundreds of kilometers down in the mantle before a kimberlite eruption carried it up intact. This episode traces how a stone of that size was moved, sold, and cut. Detectives guarded an empty safe aboard the RMS Kenilworth Castle while the real diamond traveled to London by registered mail.

For two years no private buyer would take the risk of an uncut stone. Then Louis Botha’s Transvaal government bought it for 150,000 pounds in 1907 and gave it to King Edward VII, a calculated gift from a colony Britain had just defeated in the Boer War. In Amsterdam, Joseph Asscher spent days scoring a groove, struck his blade, and watched the steel knife snap before a second blow split the stone cleanly.

• Prime Minister Henry Campbell-Bannerman advised the king to refuse the gift, while Winston Churchill lobbied for it and received a replica of the rough stone as thanks.
• Abraham Asscher carried the diamond to Amsterdam in his coat pocket by train and ferry while the Royal Navy escorted an empty box across the North Sea.
• The popular story that Joseph Asscher fainted after the cut is disputed by historian Ian Balfour and by Asscher’s nephew Louis, who said no Asscher would faint over any diamond.
• The rough yielded nine major stones and 96 minor brilliants, including the 530.2 carat Cullinan I in the Sovereign’s Sceptre and the 317.4 carat Cullinan II in the Imperial State Crown.
• Four of the rough stone’s eight surfaces were flat cleavage faces, evidence that the Cullinan was itself a fragment broken from a larger crystal that may still lie underground.