The latest sight was held between 14-29 August and generated $US370 million ($AU570.76 million). These results mark a 10 per cent decline from the sixth sight - $US411 million ($AU634 million).
The results are even more troubling compared with the seven cycle of the past year, at which De Beers sold $US638 million ($AU984.1 million) – a 42 per cent decline.
De Beers CEO Al Cook said that sightholders remain cautious.
“With the prevailing economic environment leading to softer end client demand for diamond jewellery in key consumer markets and the traditionally lower levels of midstream trading during the summer period, sightholders continued to take a prudent approach to their purchasing during the seventh sales cycle of the year,” he explained.
According to research from Tenoris, natural diamond sales in the US declined by nearly 30 per cent on a year-on-year comparison in July. This came after a 14 per cent decline in June.
"We first expected it in May, then for June and were off by a month, but it happened. The share of loose lab-created diamonds sold by US specialty retailers is at the tipping point," writes Edahn Golan.
"Of all the loose diamonds sold in July, 49.9 per cent were lab-created. Natural diamonds accounted for 50.1 per cent. At the same time, it should be noted that by value, the share of lab-created diamonds is just 25.2 per cent of diamond sales."
De Beers hosts 10 sights each year in Botswana. The next sight is scheduled for September 18-22.
More reading
De Beers CEO clarifies future plans amid dwindling sales
De Beers delays rough diamond sales as demand decreases
Pleasing demand for De Beers rough, lab-created sales surging
De Beers says lab-created diamond category ‘distinct and separate’
Diamond sales continue to slow for mining giant
Sales performance overcomes sluggish second half for De Beers
Diamond sales slump for De Beers
Weakened demand impacts De Beers sales