At its auction held this month, mining company Petra Diamonds achieved the highest price per carat in its history for a blue rough diamond, reports say. The rough is a 4.8-carat blue diamond mined from Petra’s Cullinan mine in South Africa. It sold for $1.45 million or $300,000 per carat.

The mining company which was listed on the Alternative Investment Market (AIM), recently moved up to London's main stock market.