Miners in South Africa unearthed a 232-carat white diamond that experts said could be worth up to $15 million.
London-based Petra Diamonds said the diamond was discovered at its Cullinan mine, northeast of Pretoria.
The mine is known for producing huge diamonds, including the 3,100-carat Cullinan Diamond found in 1905, the largest rough gem diamond ever found.
"The stone is ... of exceptional size and clarity, and is a magnificent example of the large, high quality diamonds for which the mine is known," Petra Diamonds said in a statement.
"We estimate a sales price in the order of $10 million to $15 million, given Gem Diamonds' recent sale of Type II white at about $70,000 per carat and assuming some losses for cutting/polishing," Numis Securities analysts said in a statement.
Markets react to news
Petra, which reported revenue of about $473 million in the previous financial year, declined to specify how much the diamond could fetch.
Petra's stock price jumped on the London stock market after the company announced the new find on Tuesday.
Petra said it expected the diamond, that has no measurable nitrogen impurities, to be sold in October-December, the second quarter of its financial year.
Investors are also awaiting the outcome Petra's sale of a rare 122.52-carat blue diamond recovered from Cullinan this year. Analysts estimated the stone's value at more than $35 million. The sale period closes on Friday.
Earlier this year, Petra sold a 29.6-carat blue diamond from the Cullinan mine for more than $25 million.
Petra has five producing mines in South Africa and one in Tanzania.
Some materials for this report came from Reuters and AFP.