In a recent report, Bain & Co. says diamond prices are poised to rise as demand grows at double the pace of supply through 2020 because of expanding middle class populations in China and India.

World demand is expected to expand an average 6.4 percent a year to almost 247 million carats by 2020 while production grows an annual 2.8 percent to 175 million carats (versus 133 million carats total output last year).

Rough-diamond prices rose 49 percent in the first half, accelerating after two straight years of more than 30 percent growth as stagnant output failed to meet Asian demand, according to data from De Beers, supplier of about a third of all rough diamonds, was among those caught on the back foot after idling mines following the global financial crisis.   De Beers Chief Executive Officer Philippe Mellier said in October that prices may “stick” at current levels after the first-half rally. Retail demand in India and China is “very, very strong” and U.S. sales are growing, defying expectations of a slide in consumption, he said. A index of overall prices has dropped 6.8 percent in the second half.     According to the Bain & Co. report, China and India will increase their share of world diamond demand to about 30 percent by 2020, from 21 percent, as middle class populations in the two countries will more than double to 469 million people and world demand will grow to $23 billion in 10 years from $12 billion last year.