The largest diamond recovered prior to this was a 16.28ct stone mined in February, which sold for US$78,947.
BlueRock said the newly found stone would soon be put to tender, with the results due on June 17.
Executive chairman Mike Houston said the record recovery was "an exciting milestone", which underpinned why BlueRock was confident about the potential of Kareevlei.
"We have a comprehensive development plan to increase production," he said.