Diamond Market, Week 40, 2026

New listings fell 34% from the prior week, dropping from nearly 7 million to 4.6 million, yet active inventory climbed to 46.6 million stones, a record across the five weeks I've tracked. That combination tells you something: the market isn't clearing. Fewer stones came in, fewer left, and the pile grew. Off-market activity dropped nearly as sharply, down 31% to 137,281 removed listings, confirming this isn't a demand surge pulling inventory down. It's accumulation. The total value sitting across the retailers I track is now $145.4 billion, also a record, up 32% over five weeks.

The spread story is the one I keep watching, and it reached a new high this week. The median price gap between the cheapest and most expensive listing for the same stone across multiple retailers hit 110.4%, up from 71.9% in week 36 and now the widest in this tracking window. Cross-retailer overlap ticked up slightly to 44.8%, so more stones are appearing at more places, but the pricing discipline among those retailers is loosening, not tightening. For buyers, that spread is an opportunity: the same stone can carry a price difference of more than double depending on where you find it.

Natural diamonds gave back ground this week. Median price per carat dropped to $2,220, down 12.2% from last week's $2,527.62, and fewer new natural stones came to market, down nearly 20% to 1.54 million. Lab-grown held steadier, with median price per carat at $448.73, off only 3.9%, and the segment now accounts for 63.5% of active inventory, essentially flat over six weeks. Lab-grown's floor isn't falling; it's grinding. The price-to-quality ratio in that segment remains exceptional for buyers who aren't anchored to natural.

Shape movement was sharp this week, particularly at the edges. Princess cut jumped 47.8% in median new listing price to $1,135, and radiant followed at +37.9% to $1,364.71, with pear close behind at +35.1% to $1,047. Round cut, which still dominated new volume at 1.81 million stones and a 39.4% share, dropped 19.3% in median price to $826. That divergence suggests the mix of what's being listed at the mid-range and premium tiers shifted this week, rather than any uniform repricing. The median active carat weight is now 1.3ct, a record high, consistent with the market accumulating larger stones.

At the very top, a 20.35ct D VVS1 pear leads the most expensive active listings at $2,855,072, followed by a 30.17ct E FL round at $2,750,336. Most intriguing is a 2.08ct fancy colour oval at $2,581,387, sitting in the top five by price despite being a fraction of the carat weight of its companions. At the other end of the size scale, the largest stone visible is a 70.28ct lab-grown cushion at $63,497, which tells you everything you need to know about where the lab-grown price ceiling sits for very large stones.

Going into week 41, the accumulation trend is the thing to watch. If new listing volumes stay well below the week 39 peak while off-market activity remains suppressed, active inventory will keep climbing and the spread will likely widen further. Natural diamond prices per carat are down 13.7% over five weeks and well below their recent peak; if that drift continues, the price-to-quality case for natural in the 1 to 2 carat range gets meaningfully more compelling.

Diamond Market Charts, Week 40, 2026 (28 September to 5 October 2026)

The five charts below summarise what the diamond market did during 28 September to 5 October 2026. Each is a static image you can save or share. Together they cover where prices sit today, how inventory is moving, the lab-grown versus natural mix, where retailers raised or cut prices, and how much the same stone can vary across competing sellers.

Lucy Market Index

Ten numbers I record every snapshot.

Counted listing rows; from October 12, 2026 we count new stones.

Versus Week 39, 2026

Biggest shape movers

Recent trends

How metrics are tracking across the recent window of snapshots.

How the Lucy Market Index has moved

By origin

Counted listing rows; from October 12, 2026 we count new stones.

Top shapes by new listings

Notable stones

Each stone links to its full Carat Hunter listing.