TORONTO • The biggest diamond ever found in North America has been unearthed by Dominion Diamond Mines and Rio Tinto Group at a mine in Canada's frozen north.

The 552-carat yellow gem was found at the Diavik mine in the Northwest Territories, and is almost three times the size of the next largest stone ever found in Canada.

While Diavik and the neighbouring Ekati mine produce some very high quality diamonds, they are not renowned for the sort of huge gems found in southern African mines.

Dominion chief executive officer Shane Durgin said the diamond is gem quality, meaning it is suitable for jewellery, but gave few additional details that help determine its value.

Yellow stones typically sell at a discount to Type IIa top whites often found in the best African mines. Still, the highest-quality, fancy vivid yellow or fancy intense yellow stones can sell for a premium.

"We can label it fancy yellow but, beyond that, due to its rough nature and the abrasions received through the processing facility, that's all we can comment on," Mr Durgin said in an interview.

"It's very hard to give a ballpark estimate. It all depends on, again, the cutting and the resulting stone it ends up (as)," added Mr Durgin.

The discovery is the seventh-biggest this century, according to Bloomberg calculations, and would be among the 30 largest stones ever unearthed.

The biggest was the 3,106-carat Cullinan, found near Pretoria in South Africa in 1905.

It was cut into several polished gems, the two largest of which - the Great Star of Africa and the Lesser Star of Africa - are set in the crown jewels of Britain.

There have been a slew of big finds in recent years as better technology helped miners first detect, and then not break big stones that are susceptible to being smashed in the mining process.

Among those are diamonds found by Lucara Diamond and Gem Diamonds that fetched between US$40 million (S$55 million) and US$63 million (S$86 million).

BLOOMBERG