A Canadian mining company says it has discovered the largest gem-quality diamond ever found in North America, a yellowish stone roughly the size of a small chicken egg.

The 552-carat stone, found in a mine in Canada's Northwest Territories near the Arctic Circle, is nearly three times the size of the previous record holder, a 187-carat gem called the Foxfire, Dominion Diamond Mines said in a statement Saturday.

"A diamond of this size is completely unexpected for this part of the world," said Dominion, 40 percent owner of the mine. It called the find "astonishing."

The stone is thought to be one of the 30 biggest diamonds ever found.

Dominion said the rough stone -- with some abrasion markings on its surface due to "the difficult journey it underwent during recovery" -- would be polished and cut by a master cutter before its ultimate value can be determined.

The Foxfire, which came from the same Diavik mine, was said to glow bright blue in the dark.

The huge gem was exhibited at a Smithsonian museum in Washington along with the iconic Hope Diamond before being cut into two stones and sold for $1.3 million.

The largest diamond ever found was a 3,100-carat monster, the Cullinan, unearthed in South Africa in 1905. It was ultimately cut into nine major stones and 96 smaller ones.