RAPAPORT... De Beers lifted prices of select goods at last week's sight, reflecting strong rough trading and improving demand in the corresponding polished categories, industry insiders told Rapaport News.Prices climbed by 1% to 2% for 0.75-carat rough goods and larger, as well as for -7 sieve sizes, sources said following the December sale. The miner also adjusted assortments, making some boxes seem more expensive than in previous sales, but prices were still higher on a like-for-like basis, they explained. "They increased prices in the areas where the underlying polished was moving," a source said Sunday. "Assortments also improved, but we don't think that assortments improved to the degree that the prices increased."The market for relatively large polished has picked up in the fourth quarter, with the RapNet Diamond Index (RAPI?,,?) for 1-carat stones gaining 1.6% since October 1, and RAPI for 3-carat stones jumping 4.8%. That contrasts with a weaker market for 0.30-carat polished."Because of Covid-19, the factories aren't working in full swing, and the smaller sizes require more workers," making them less desirable among manufacturers, a sightholder said on condition of anonymity. "Also, all over the world, demand for 50 points and up is very high."However, dealers raised concerns that some of the rough trading was speculative, with sightholders estimating rough prices across the industry had risen by up to 10% in the past month. The increase in polished prices has been more moderate, and retailers already have the diamonds they need for the holidays, they observed."People are buying goods even if they're not worth the money, because they're being offered premiums in advance," one De Beers customer said. "The rough market is on fire."Price increases at De Beers sight have been few and far between in recent years: The company's rough-price index fell 6% in 2019 and slumped 8% in the first half of 2020, when coronavirus lockdowns caused a market slump. The company reduced prices at the August and September sights in a bid to spur demand once trading started to improve.A De Beers spokesperson declined to comment.