De Beers, the world’s biggest diamond producer, said sales of the gems at its most recent auction fell to the lowest this year. The company, owned by Anglo American Plc, sold $470 million of diamonds in the ninth cycle, compared with $494 million at its previous offering, it said in a statement.

The diamond industry is seasonal, with the holiday period from Thanksgiving in November through the Lunar New Year in Asia in January or early February typically the busiest period for jewelry sales. De Beers’ customers tend buy more rough stones earlier in the year to prepare for this period.

While rough-diamond prices gained 7.4 percent this year, Anglo CEO Mark Cutifani and other executives have cautioned that the final six months of 2016 could be more difficult for the industry.