Petra Diamonds putting a 507-carat egg-sized diamond on sale this week, which it discovered at its Cullian mine in South Africa. The company is expecting the 100-gram diamond to sell for around $25 million, reports say. Originally, analysts had placed the diamond price at around $20 million, but the rising rough diamond prices and higher buyer interest cited for the stone, could raise the diamond’s sale price, reports add.

The stone is one of the 20 largest high-quality rough diamonds ever to be found, reports say. Its sale will enable the company’s annual financial results to be spurred. The stone is named as the Cullinan Heritage.