(IDEX Online) - A "once in a lifetime" 29.52-carat pink diamond, recovered from the banks of the middle Orange River, in South Africa, is being sold tomorrow (30 June).The Type II rough diamond, said to have an "unusual depth of color and exceptional clarity" and has been named Protea Pink, after South Africa's national flower.It is believed to have originated in the Lesotho kimberlites 90m years ago, says Lyndon de Meillon, geologist at Pioneer Diamond Tender House, in Johannesburg, which is selling the stone.He says it was probably carried 500km down river to an ancient river terrace where it was trapped. The gem was recovered by a junior alluvial miner earlier this year.The middle section of the Orange River - South Africa's longest river at over 1,500 miles - has the highest average value per carat in the world, but the lowest grade in carat per hundred tonnes of any area actively mined, said de Meillon.Pic courtesy Pioneer Diamond Tender House