LONDON - A rare 122.52-carat blue diamond found in South Africa could fetch more than $35 million for a London-listed mining company. Only three or four blue diamonds over 100 carats have ever been recovered, according to Cathy Mallins, corporate communications manager at Petra Diamonds Ltd. So far, the highest price on record for a rough diamond is $35.3 million, paid in February 2010 for a 507-carat white stone recovered from the same mine, finnCap analyst Martin Potts said in a research note. “We think that this stone may break that record,” he said. oth diamonds were recovered from the Cullinan mine, the source of many large diamonds, including the largest rough gem diamond ever recovered - the 3,106-carat Cullinan Diamond found in 1905.