At 54 carats, it is expected to curry a great deal of interest when it goes on sale in September.
Fancy intense yellow and fancy vivid yellow diamonds tend to cost more than colourless stones because of their rarity.
Last year Dominion Diamond Mines unearthed a 552-carat yellow diamond from its Diavik Diamond Mine in Canada.
De Beers & Tiffany
Among the world's largest of this ilk is the 440-carat light-yellow diamond that was found by De Beers in 1888 and later cut into a 235-carat cushion-cut stone.
The Tiffany Yellow Diamond is also ranks up there. It weighted 287 carats in the rough when it was found in 1878 in the Kimberly Mine in South Africa.
Of his company’s discovery, Firestone chief Paul Bosma said: "The Liqhobong mine has become known for its fancy yellow stones but this one is the largest we've recovered so far and is therefore quite special.
“Although certain segments of the diamond market are currently struggling, the demand for unique natural stones remains positive."