(IDEX Online) - BlueRock has announced the recovery of a 21.56-ct diamond at its Kareevlei mine, in South Africa.It's the company's biggest ever rough stone, and is likely to become its most valuable when it is sold at tender later this month.The "exceptional quality" stone is expected to fetch significantly more than $236,000, the company's current record, set by a 20.7-ct diamond in October 2019. It's described as "a high-quality, D-colored round diamond with high-value recovery options". Meanwhile the London-listed miner has revised down guidance on output after unrest in South Africa delayed ongoing work to expand the mine.It now expects to produce between 24,000 cts and 28,000 cts this year, rather than 30,000 cts to 39,000 cts, but says annual revenue should remain unchanged at $11m because prices are high.Pic shows Kareevlei processing plant