De Beers, the world's largest diamond producer, suffered a drop in sales during its most recent cycle.
The South African company said it sold nearly £250 million of rough-cut diamonds, down from £302 million in its previous cycle and lower than the £360 million in the same period a year prior.
It comes as its owner Anglo American PLC (LSE:AAL) rejected a takeover by rival mining giant BHP Group Ltd (LSE:BHP, ASX:BHP).
Anglo suffered a 31% slump in underlying earnings during the past financial year, and blamed the drop on a slump in commodities after it wrote down around US$2.4 billion for its diamond and nickel divisions.
Earlier this month, Anglo American said it had begun a massive restructuring including the divestment of its metallurgical coal (met coal) assets, following a rebuffed £39 billion bid approach from BHP.
Part of this restructuring includes plans to sell De Beers "in a responsible and orderly way".