The 1,111-carat stone was recovered from its karowe mine,about 500km (300 miles) north of the capital,Gaborone.
It is the biggest diamond tobe discovered in Botswana and the largest find in more than a century.
The 3,106-carat Cullinan diamond was found in south Africa in 1905 and cut into nine separate stones,many of which are in the British Crown Jewels.