COLOMBO, Sri Lanka (AP) — A gem company in Sri Lanka has unveiled a rare and massive gemstone weighing 683 pounds (310 kilograms) that has been certified as one of the biggest corundums ever found in the country.

Sri Lanka's National Gem and Jewelry Authority says it has done a series of gemological tests on five samples taken from the rock.

“To our knowledge this specimen is indeed a rare specimen and not recorded in the geological literature," read an authentication letter given by the authority to the owners who unveiled the stone on Sunday.

When the outer layer was removed for inspection, the interior showed a silky blue patchy appearance, the letter said, suggesting the stone is a blue sapphire.

Shanka Ruwanditha, a director of the company that currently owns the massive stone, the Gemological Institute of Ratnapura, told The Associated Press on Monday that the owners plan to obtain the services of a local or foreign gem valuer soon to determine the price of the rock.

Sri Lanka and especially its southwestern city of Ratnapura, or the Gem City in the local language, has been known for centuries for mining gems and precious stones.