Two unheated sapphires sold in the same Paris room on October 29. Per carat, one went for 5.7 times the other. If a client walks in with one of those numbers next week, you will want to know what it actually measures. That is this week's focus, with Geneva right behind it.

Key Takeaways

→ Milan, a Kashmir ring at 2.8x. Sotheby's Fine Jewelry and Watches sale in Milan on October 28 totaled €6.9 million ($7.7 million) across more than 280 lots. It included a cushion-shaped 6.40-carat Kashmir sapphire in a diamond surround, at €281,600 ($313,432). That is about $48,974 per carat for the whole ring (our arithmetic). A Cartier emerald cabochon necklace made €256,000 against €40,000 to 60,000 (Rapaport).

→ Paris, a Cartier sapphire at 3.4x. At Bonhams Paris on October 29, lot 149, a Cartier ring set with a sapphire of about 11.5 carats, sold for €205,400 including premium. The Bellerophon report, dated September 30, calls it a natural sapphire from Madagascar, with no indication of treatment, that can be described as "Royal Blue" in the trade. About $20,035 per carat at Rapaport's conversion (our arithmetic).

→ Same sale, an unheated Ceylon sapphire for much less. Lot 190, a Chaumet ring with a sapphire of about 13.70 carats, sold for €42,840. SSEF calls it Sri Lankan with no indication of heating. About €3,127 per carat, against about €17,861 for the Cartier ring (our arithmetic). More on that gap below.

→ GIA buys an inclusion library. GIA acquired John Koivula's collection of gem and mineral inclusions, 2,665 lots (Rapaport, November 3). Inclusions are among the main clues labs use to determine origin and treatment.

→ Gübelin opens a drop-off in Dubai. Gübelin set up a "Take-In Window" in Dubai's Almas Tower. Stones are received there and shipped to Switzerland for testing (Rapaport, November 1). No opening date was given.

The index tracks the 8 reference stones every week. Each row holds until a new dated transaction moves it. No row moves this week.

Auction results and producer averages. Tsavorite and tanzanite are trade benchmarks. Not retail. Sources: Christie's, Sotheby's, Gemfields, Bonhams, GemGuide, Pala International.

Notable this week: the Milan Kashmir ring works out to about $48,974 per carat, roughly a third of our sapphire row. The stone is less than half the weight, and the row stays where it is. The ruby row keeps its "policy watch" flag while Mozambique's 20 percent rule is unclear.

One more print from Bonhams Paris, for scale: lot 48, an 81.17-carat "Paraíba-type" tourmaline pendant, sold for €64,600, inside its estimate. About $893 per carat (our arithmetic). The lot page gives no origin, so it says nothing about our Brazilian Paraíba row.

The two lots. Bonhams Paris, October 29. Lot 149, a Cartier ring, Madagascar sapphire of about 11.5 carats, no indication of treatment (Bellerophon). Lot 190, a Chaumet ring, Sri Lankan sapphire of about 13.70 carats, no indication of heating (SSEF, with an IGI report too).

The prices. €205,400 for the Cartier ring, €42,840 for the Chaumet ring. Per carat, about €17,861 against €3,127, a gap of 5.7 times (our arithmetic).

What the catalogue shows. Four differences you can read on the lot pages. The maker, Cartier or Chaumet. The origin, Madagascar or Sri Lanka. The cut, oval or octagonal step-cut. The wording, since the Cartier stone's report adds that it can be described as "Royal Blue" in the trade.

What it does not show. How the two colors compare side by side, since the Chaumet lot text describes no color at all. How well each stone is cut. Who bid. We cannot tell which of the differences drove the price, and we will not guess.

Why it matters to you. Both prices are for finished rings, with mounts and diamonds. When you divide a jewel's price by the stone's carats, the result folds in the signature, the setting and the side stones. Use it as a jewel price, not as a loose-stone benchmark.

What to ask when a client quotes an auction price. Three questions, in this order. Was it a loose stone or a signed jewel? Which lab, and what does the report say about treatment? Is the figure hammer or including premium? The Cartier and Chaumet lot pages answer all three. Open the page before you quote.

1. Two prints are not a trend. The Milan Kashmir and the Paris Cartier both cleared their estimates by a wide margin, in two cities, in two days. Estimates usually exclude the buyer's premium, so these multiples run a little high. Geneva brings several major sapphires and rubies to auction next week. That is the real test.

2. Divide carefully. A per-carat figure on a signed ring is not the same number as a per-carat figure on a loose stone. Check what the price covers before you compare.

3. Read the whole report line. A trade-color term such as "Royal Blue" is the issuing lab's call. Note which lab wrote it, not only the words.

→ Christie's Geneva, November 10. Lot 562, a ring with a 23.72-carat Kashmir sapphire, SSEF and Gübelin reports, no indication of heating, estimated at CHF 1.25 to 2 million. At the high estimate, about CHF 84,300 per carat (our arithmetic). Lot 609, a Van Cleef & Arpels brooch with a 43.94-carat unheated Sri Lankan sapphire (Gübelin), CHF 300,000 to 500,000 (Christie's).

→ Sotheby's Geneva, November 11. The 197.80-carat unheated Ceylon "Romanov Sapphire", estimated at CHF 850,000 to 1.7 million, or $1 to 2 million (National Jeweler). At the high estimate, about $10,100 per carat. The same day, a 5.027-carat "pigeon blood" ruby ring at CHF 850,000 to 1.3 million, about CHF 258,600 per carat at the high end (JCK). Per-carat figures are our arithmetic.

→ Sotheby's Geneva Fine Jewelry, November 13. A 25.87-carat Ceylon sapphire ring with a high estimate of CHF 170,000 (Rapaport).

→ Christie's Hong Kong, November 24. The 21.05-carat Kashmir sapphire Cartier ring, estimated at up to $6.4 million (Rapaport).

→ Gemfields' December Trade Select ruby auction. The next ruby auction Gemfields has announced.

We report results, not estimates. Most of these Geneva sales end after next Tuesday, so their results go into the November 17 edition.

Pick one colored-stone lot from the Geneva sales. Write down its high estimate and divide it by the carat weight. When the sale ends, put the result next to it and see how far the room moved.

— Carat Brief

Carat Brief is editorial. Nothing here is investment, legal, or tax advice. Gemstones are illiquid and require certified verification before purchase. Work with credentialed labs: GIA, AGL, SSEF, Gübelin, Lotus Gemology.

Sources: Rapaport (Sotheby's rakes in $7.7M at Milan auction, October 29, 2026); Bonhams lot pages, Fine Jewellery Paris sale 31785, lots 48, 149 and 190, and Bonhams press release; Rapaport (Cartier sapphire ring more than triples high estimate at Bonhams, November 2, 2026); Rapaport (GIA obtains unique assortment of gem and mineral inclusions, November 3, 2026); Rapaport (Two European labs open grading facilities in Dubai, November 1, 2026); Christie's (Magnificent Jewels Geneva preview, October 30, 2026, and lot 562 page); National Jeweler (197-carat Romanov sapphire heads to Sotheby's Geneva, November 2, 2026); JCK (Sotheby's Geneva sale, October 28, 2026); Rapaport (26ct sapphire to headline Sotheby's Geneva auction, November 1, 2026); Rapaport (Christie's predicts $6M payday for Cartier sapphire ring, October 20, 2026); Gemfields. Derived figures are marked as our arithmetic. Euro to dollar conversions are Rapaport's.