Cullinan Mine
Cullinan Mine
South Africa's premier source of large Type IIa and rare blue diamonds
The Cullinan Mine, situated approximately 40 kilometres east of Pretoria in Gauteng Province, South Africa, is among the most consequential diamond-producing operations in recorded history. Discovered in 1902 and originally known as the Premier Mine, it was renamed in 2003 to honour the site's most celebrated find: the 3,106-carat rough diamond recovered in 1905 that bears the same name. The mine is currently operated by Petra Diamonds and exploits a kimberlite pipe of exceptional scale, covering some 32 hectares in plan — one of the largest kimberlite pipes known. Its geological character consistently yields large, gem-quality stones of rare purity, making it a benchmark locality in the global diamond trade.
Geological Character
The Cullinan kimberlite pipe is classified as a Group I kimberlite and is distinguished by its unusually high proportion of Type II diamonds — stones that contain no measurable nitrogen impurities within their crystal lattice. Type IIa diamonds, which are essentially chemically pure carbon, are colourless to near-colourless and frequently attain exceptional transparency and size. Type IIb diamonds, which contain trace boron in place of nitrogen, are electrically semi-conductive and display the blue-to-grey hues associated with some of the world's most celebrated coloured diamonds. Cullinan is one of very few mines on earth known to produce both Type IIa and Type IIb material in commercially meaningful quantities. The pipe extends to considerable depth, and successive mining phases — open-pit followed by underground block-caving methods — have progressively accessed deeper ore zones that continue to yield large rough crystals.
Historical Background
The mine was established by the Premier (Transvaal) Diamond Mining Company, with Thomas Cullinan, a Johannesburg property developer, instrumental in its founding. Within three years of opening, the mine produced the largest gem-quality rough diamond ever recorded: the Cullinan diamond, weighing 3,106.75 carats, recovered on 26 January 1905 by surface manager Frederick Wells. The Transvaal government purchased the stone and presented it to King Edward VII, after which it was entrusted to the Amsterdam firm of Asscher Brothers for cleaving and polishing. The resulting nine principal stones — designated Cullinan I through Cullinan IX — are now set in the British Crown Jewels or held in the Royal Collection. Cullinan I (530.20 carats, pear shape) remains the largest polished colourless diamond in existence and is mounted in the Sovereign's Sceptre with Cross.
For much of the twentieth century the mine operated under the De Beers group. Petra Diamonds acquired it from De Beers in 2008, a transaction that transferred stewardship of one of the industry's most storied assets to a mid-tier producer focused on exceptional-quality output rather than volume.
Notable Stones
Beyond the Cullinan diamond itself, the mine has produced a remarkable succession of exceptional rough and polished stones:
- Cullinan Heritage — a 507.55-carat Type IIa rough recovered in 2009, sold to Chow Tai Fook for approximately US$35.3 million, at the time a record price per carat for a rough diamond at auction.
- Cullinan Dream — a 24.18-carat fancy intense blue polished diamond, sold at Christie's New York in 2016 for approximately US$25.4 million.
- Blue Moon of Josephine — a 12.03-carat fancy vivid blue diamond polished from a 29.6-carat Cullinan rough, sold at Sotheby's Geneva in 2015 for approximately US$48.5 million, then a world record price per carat for any gemstone at auction.
- Numerous large colourless Type IIa roughs exceeding 100 carats have been recovered across the mine's operational history, several of which have been polished into stones of significant auction and private-sale importance.
In the Trade
Within the diamond trade, a Cullinan provenance carries meaningful weight. The mine's consistent association with large, high-clarity, Type IIa material means that rough parcels and individual crystals originating there command attention at tender. Petra Diamonds sells exceptional stones through a formal tender process rather than through the De Beers sightholder system, allowing competitive bidding that has at times established benchmark prices. The mine's blue diamonds in particular are regarded as among the finest in the world, comparable in saturation and purity to the storied blue diamonds of the Golconda era. Major auction houses — Sotheby's, Christie's, and Bonhams — have each handled polished Cullinan-origin stones at the top of their sale calendars. Laboratory reports from the Gemological Institute of America (GIA) and other leading bodies routinely note Type II classification and, where traceable, origin data that supports Cullinan provenance.
Petra Diamonds has also pursued a responsible-sourcing narrative around the mine, given its location within a stable jurisdiction and its long-documented production history — factors increasingly valued by high-end jewellery houses seeking transparent supply chains.