Mwadui — The Williamson Diamond Mine, Tanzania
Mwadui — The Williamson Diamond Mine, Tanzania
The Shinyanga kimberlite that produced the Williamson Pink and remains one of the world's largest pipes by surface area
Mwadui, also known as the Williamson Mine, is a diamond mine in the Shinyanga Region of north-central Tanzania, discovered in 1940 by the Canadian geologist John T. Williamson. The deposit is one of the largest diamond-bearing kimberlite pipes in the world by surface area — roughly 146 hectares — and has produced both commercial-grade diamonds and a small but significant population of fine fancy-pink stones. Its most famous product is the 54.5-carat rough that became the Williamson Pink.
Geology and discovery
The Mwadui pipe is a kimberlite intrusion of late Cretaceous age that surfaces as a low-grade, large-tonnage deposit. Williamson, working as an independent geologist after time at the De Beers operation in South Africa, identified the pipe in 1940 and developed it through the 1940s and 1950s as the Williamson Diamond Mine. The deposit's surface area and accessibility supported open-pit operation; grades are modest but workable at scale.
Operation and ownership
After Williamson's death in 1958, ownership passed first to the Tanganyikan and Tanzanian governments and later into joint operation with De Beers. In the 2000s the mine came under Petra Diamonds in joint venture with the Tanzanian state. Production has been intermittent in recent years, with periods of suspension related to ownership disputes and operational reviews.
The Williamson Pink
The mine's signature stone is the Williamson Pink, a 54.5-carat pink rough recovered in 1947 and presented by John Williamson to the future Queen Elizabeth II as a wedding gift. Cut by Briefel and Lemer in London to a 23.6-carat round brilliant, the polished stone was set in a Cartier flower brooch in 1953 and remains in the British royal collection. Mwadui has produced other fine pinks since — recent recovery of a larger pink rough in the 2020s drew international press — and the deposit is recognised as one of a small handful of sources for natural-coloured pink diamonds.
Trade significance
For the broader diamond market, Mwadui is one of several African producers and does not carry an origin premium — diamond pricing is dominated by the 4Cs rather than source. For pink-diamond connoisseurs, however, Mwadui sits alongside Argyle (closed 2020), Golconda (historical), and certain Russian sources as a rare provenance worth specific note when a stone can be tied to it through laboratory documentation or chain-of-custody records.