The 1,111 carat diamond is gem quality and is a Type IIa diamond.
The Royal Collection Trust, which oversees British royal treasures, says the largest diamond ever found was the 3,106-carat Cullinan diamond, unearthed in South Africa in 1905.
That diamond was cut into smaller pieces that are part of the crown jewels.
Lucara, which is based in Vancouver, says it also found two other large white diamonds in the same mine, Karowe, in Botswana. Those diamonds measure 813 carats and 374 carats.