Lab-grown diamond prices fell 11% in the month to October 18, according to StoneAlgo's index, and are down 27% over the year. The monthly figure is the more significant of the two. A 27% annual decline is consistent with the steady erosion the category has shown in recent years. An 11% decline in a single month means a large share of the year's loss has come in the last four weeks alone.

At the same time, natural diamond prices in smaller sizes have been firming. The divergence is now wide enough that retailers setting holiday assortments face two very different pricing problems in the same showcase.

The Asking-Price Gap

StoneAlgo's asking-price data as of October 14 put a one-carat lab-grown diamond at an average of $502, against $3,820 for a natural stone of the same weight. A second source runs higher. Clairamor's picker, as of October 19, listed a one-carat lab-grown stone at $640, a two-carat at $1,138 and a three-carat at $1,865.

The comparison with StoneAlgo's natural average is sharper still. At one carat, the $502 lab-grown average is a fraction of the $3,820 natural figure. Retail jewelers who priced lab-grown engagement rings on a fixed markup over cost a year ago are now selling into a market where the index for the center stone is 27% lower.

Two features of the Clairamor figures stand out. First, the one-carat price of $640 sits above StoneAlgo's $502 average, a reminder that lab-grown pricing varies by source and that no single benchmark has the authority the Rapaport Price List carries for natural goods. Second, price does not scale with weight the way it does in natural diamonds. A three-carat lab-grown stone at $1,865 costs less than three times the one-carat price of $640. In natural goods, per-carat prices typically rise with size, so a three-carat stone costs considerably more than three one-carat stones. Lab-grown has largely abandoned that premium.

For retailers, the practical consequence is that the size upsell, historically one of the most reliable margin levers in bridal, works differently in lab-grown. A customer moving from one carat to three carats in lab-grown, on Clairamor's figures, goes from $640 to $1,865. In natural goods the same step is measured in multiples of the $3,820 one-carat average.

Natural Small Goods Firm

The natural side of the market moved the other way in September. Rapaport USA reported on October 6 that its 0.30-carat index rose 3.2% for the month and its 0.50-carat index rose 2.5%. The 1-carat index rose 0.3%, while the 3-carat index advanced 1.5%. The strength in small goods was reflected in the Rapaport Price List itself, which increased on September 11 for certain round, 0.30- to 0.69-carat, D-G, VVS1-SI1 diamonds.

The pattern fits a reading in which lab-grown has taken much of the price-sensitive demand at one carat and above, leaving natural small goods, used in fashion jewelry, side stones and smaller engagement rings, with steadier demand. The 1-carat index, at 0.3%, was the weakest of the four sizes reported, and one carat is where the two products compete most directly.

Rough Supply

On the upstream side, De Beers generated consolidated revenue of $731 million from two sights in the third quarter of 2026, according to the Q3 production report released October 20. Reported carat volumes for the quarter differ between summaries of the release, so the revenue figure is the firmer guide.

Two sights in a quarter indicates continued supply discipline from the largest producer. With natural small goods firming and the Rapaport list moving higher in the 0.30- to 0.69-carat range, the midstream has some evidence that controlled rough supply is supporting polished prices at the smaller end. Whether that holds through the holiday season will depend on retail sell-through, which our industry coverage tracks in this week's report on the October show calendar.

Implications for Holiday Inventory

Retailers stocking lab-grown for the holiday quarter carry a specific risk. A product that lost 11% of its index value in one month can lose more between purchase and sale. Memo terms, shorter reorder cycles and smaller opening positions limit that exposure. Natural goods carry the opposite problem: steadier prices, but higher capital commitment per stone, with a one-carat natural averaging $3,820 on StoneAlgo's asking prices.

Gold adds a further variable for finished jewelry pricing. Spot fell 3.08% on October 30 to $3,897.48 an ounce, as detailed in our gold desk report, which will ease metal costs on mountings if it holds. The wider week is summarized in the October 30 trade wrap.

The open question for the first quarter of 2027 is where lab-grown finds a floor. At $502 for an average one-carat stone on StoneAlgo's data, and with the index down 11% in a single month, the category is now priced closer to fashion jewelry than to bridal. If the next monthly reading shows another double-digit decline, how many retailers will continue to merchandise lab-grown as an engagement product?