It is reported that the mining group Petra Diamonds has discovered a 507.55-carat white diamond at South Africas famed Culinan mine, one of the largest high-quality rough diamonds ever discovered. According to Johan Dippenaar, CEO, Petra Diamonds, the diamond weighs just over 100 grams and is believed to be a rare type II diamond with exceptional colour and clarity. The precious stone was found alongside three other special white gems of similar colour and clarity, a large diamond of 168 carats and two other stones 58.5 and 53.3 carats. The gem is valued at upwards of USD $ 20 million.