From BBC News:
The 29.6-carat stone was recovered by Petra Diamonds at its Cullinan mine, about 40km (25 miles) north-east of Pretoria.
"This stone is one of the most exceptional stones recovered at Cullinan during Petra's operation of the mine," the company said.
... "The stone is an outstanding vivid blue with extraordinary saturation, tone and clarity, and has the potential to yield a polished stone of great value and importance," Petra said in a statement on Tuesday.
... In 1905, the renowned Star of Africa blue diamond - the world's second largest cut diamond - was discovered at the Cullinan mine.
The pear-shaped 530-carat stone was presented to King Edward VII and became part of the British crown jewels.