The diamond was recovered with a 22ct makeable white stone, and an 11ct fancy light-pink stone.
Firestone said it would sell the diamonds in May at the next tender.
CEO Paul Bosma said the company had a good weekend, with the recovery of three large stones from within the northern, lower-grade part of the pit.
"These recoveries will certainly assist in supporting the average value of the next sale in May," he said.
In February, Firestone recovered a 70ct white, makeable stone in the same part of the pit, which was sold in its March tender.
