Rare 158-Carat Yellow Diamond Unearthed After 2 Billion Years Beneath Canada's Arctic

In March 2025, miners at one of North America’s most isolated mining sites extracted a remarkable yellow diamond from the icy terrains of Canada's Northwest Territories. Weighing in at 158.20 carats, this gem dates back nearly two billion years. Rio Tinto revealed the discovery on April 1, confirming it ranks among the largest gem-quality yellow diamonds ever uncovered in Canadian soil.

The discovery came from the Diavik mine, located on a small island in Lac de Gras roughly 200 kilometers south of the Arctic Circle. Accessible only by ice roads in winter and by floatplane during summer, the mine relies exclusively on the public power grid. The retrieval of such a high-grade diamond from this remote region highlights the significance of the find.

The Rare Chemistry Behind Yellow Diamonds

Yellow diamonds are exceptionally uncommon at Diavik, where less than one percent of the total gems display any yellow hue, the vast majority being clear, white stones. The 158.20-carat gem is only the fifth yellow diamond exceeding 100 carats discovered at Diavik over its 22 years of operation.

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The distinct yellow color arises due to nitrogen atoms trapped within the diamond’s crystal structure while it forms. When these atoms group together rather than disperse, they absorb blue light, resulting in the yellow coloration. Such diamonds originate from environmental conditions that no longer occur on Earth today.

Matt Breen, Chief Operating Officer at Diavik Diamond Mines, described the gem as “a marvel of nature and a tribute to the resilience and expertise of the men and women working in Diavik’s demanding sub-Arctic conditions.”

Ranking Among Canada’s Largest Diamonds

Although impressive, this gem is not Diavik's largest. That distinction belongs to a 552.74-carat yellow diamond found in 2018 at the same mine, roughly the size of a chicken egg and recognized as the largest diamond ever discovered in North America. Earlier, the 187.7-carat "Foxfire"—another Diavik find in 2015—held the record.

The 552-carat fancy yellow diamond. Image credit: Rio Tinto

This recent find adds to a prominent selection of significant diamonds extracted across the continent. Part of Diavik’s appeal lies in its verifiable Canadian origin, a factor increasingly valued by buyers. Patrick Coppens, General Manager of Sales and Marketing at Rio Tinto Diamonds, expressed eagerness to “track the remarkable path of this extraordinary diamond,” referring to its assessment, cutting, and eventual market debut.

Final Major Discovery as Diavik Nears Closure

Originally slated to close in 2025, Diavik's life was extended when Rio Tinto invested in underground mining at one of its kimberlite pipes called A21. Production started there in late 2024 and is expected to continue into early 2026. The 158.20-carat yellow diamond was uncovered during this closing phase.

It’s important to note that while Rio Tinto referred to the diamond as "two billion years old," geological experts highlighted that the kimberlite pipe transporting the gem to the surface is much younger—around 50 million years old. The two-billion-year figure pertains to the ancient Precambrian bedrock surrounding the pipe.

Estimates place Diavik’s kimberlite formations up to 1.27 billion years old. Rio Tinto's statement reflects the geological origin of the diamond itself rather than the age of the conduit that brought it up.

Cutting Challenges and Unrevealed Valuation

Operating off the grid since its inception, Diavik has utilized a hybrid wind-diesel system since 2012. A new solar energy facility was completed in 2024, further decreasing diesel use in this environmentally fragile setting.

The value of the 158.20-carat yellow diamond remains undisclosed, and Rio Tinto has not announced a buyer. Transforming such a sizeable rough stone into a polished gem is a meticulous task, often resulting in more than half its original weight being lost as cutters enhance its size and color intensity.

Diavik officially closed on March 24, 2026, marking the 158-carat yellow diamond as the final significant gem uncovered over the mine’s 22-year history.