While the overall diamond market is recovering after De Beers SA and PJSC ALROSA cut supply in 2015, the smallest and the lowest-quality gems were left behind, Bloomberg News reported Sept. 28.
The prices of the smallest diamonds were down 15% this year, compared with a 7% rise for all stones.
Petra Diamonds Ltd. CEO Johan Dippenaar partly blamed the price slump for gems smaller than 0.75 carat to a hangover of producer stockpiling, which left a "hefty supply" to sell in the first half.
Meanwhile, consultant Gemdax said manufacturers preferred bigger, higher-quality stones that can be bought and sold faster.
The rise of man-made diamonds also threatens cheaper stones the most, according to the report.
Among small diamonds, fine quality gems outperformed the so-called commercial stones.