Petra Diamonds Limited has discovered a 507.55 carat spectacular white diamond from its Cullinan mine in South Africa, reports say. Although the stone is under analysis by experts, its initial verification reveals that it figures as a Type II diamond of exceptional colour and clarity. Apart from this stone, there have been previous discoveries of three exceptional white stones of similar colour and clarity in the same production run; one of 168.00 carats and two of 58.50 and 53.30 carats, respectively.