A mineworker walks towards a shaft at the Cullinan diamond mine, which continues to be a source of large gem diamonds and rare blue diamonds. Cullinan earned its place in history with the discovery of the Cullinan diamond in 1905, the largest rough diamond, at 3 106 ct, ever found, which was cut for use in the British crown jewels. Cullinan continues to produce world-class diamonds under the stewardship of the London-listed Petra Diamonds, which last week appointed Richard Duffy as its new CEO.