Diamond prices fell in October, unevenly. The sharpest falls were in the smallest polished stones, which had gained most earlier this year, and they came with more stones on offer, not fewer. The news is about supply: small natural polished built up after a strong run, in the same week a report put last year’s lab-grown production at a record.
Rapaport’s November 3 release gave the natural figures. Its asking-price index for round, D to H, IF to VS2 diamonds fell 5.5 per cent for 0.30-carat stones and 2.3 per cent for 0.50-carat stones in October, after a late-September peak. The 1-carat index fell 0.9 per cent; the 3-carat rose 0.9 per cent. The 0.30-carat index is still up 8.8 per cent this year: October reversed part of a rise, not all of it.
That index needs handling carefully. RAPI is the average asking price of the 10 per cent lowest-priced rounds in each of its top quality categories, GIA-graded, offered on Rapaport’s platform. It records what sellers ask in a defined slice of the market — not completed sales, and not the price on any stone offered to a bench.
The listings show why direction changed. Listings of 0.30-carat rounds in those qualities grew 165 per cent between June 1 and November 1, with similar, less sharp rises in 0.40- to 0.99-carat rounds, and prices came under pressure as inventory rose. Rapaport offered two possible reasons: manufacturers had cut more of those sizes after the April-to-September recovery, and some cutters may have sought grading reports for 0.30-carat stones again after skipping certification when prices were lower. Both concern stones made and listed, not buyers disappearing.
Larger sizes underline the point. Demand for 1-carat diamonds was stable to soft, goods of 2 carats and above held steady, and recent declines in oval prices eased as supply fell. Where supply rose, prices softened; where it fell or held, they steadied.
The lab-grown figures describe the other supply. In a report dated November 1, prepared with Eyal Axelrod of Lexa International and reported by JCK on November 3, analyst Edahn Golan estimated global production of gem-quality lab-grown diamonds at a record 69.4 million carats in 2025 — about 30 per cent below the 98.8 million carats of natural rough mined. Global retail sales of lab-grown diamond jewellery were an estimated US$23.8 billion (about C$33 billion). Retailers’ unit purchases of finished lab-grown jewellery rose 33 per cent, against a 25 per cent rise in unit sales: another inventory build, in the other material.
The two builds are not the same event, and neither source reported one causing the other. Small natural polished accumulated because more was cut after a recovery, and more was certified and listed. Lab-grown output set a record because factories expand by capacity and decision. What they share is the pressure: more stones than previous asking prices could carry.
For a bench buying polished stones one at a time, the reading is narrow. An index down 5.5 per cent does not cut the invoice on a specific stone by 5.5 per cent; that stone is priced when offered, on its grade and report. And record lab-grown production does not change what a natural stone is: where it formed, how it was mined and cut, and what its report says remain facts about that stone, whatever volume is grown elsewhere.
— Tom