The provisional value from global sightholder and auction sales was down from $500 million in the first cycle of the year and also lower than the second cycle of 2018's $563 million.
It was also the lowest value since the ninth cycle of 2018 when $442 million worth of rough stones were sold.
CEO Bruce Cleaver said while overall demand for lower value rough diamonds had remained subdued, the company had seen an increase in demand from India as factories began to restock.