A 73-Carat Yellow Diamond Just Stole the Spotlight at Sotheby's — Meet "The Sienna Star"

73 Carats of Pure Canary Fire — and It Goes Under the Hammer Tomorrow.

On the morning of June 9, 2026, at Sotheby's New York Magnificent Jewels sale, a diamond the size of a small grape will cross the block. It is called The Sienna Star, and at 73.11 carats it is one of the largest Fancy Vivid Yellow diamonds ever to come to auction. The pre-sale estimate runs as high as $3 million. The previews opened to collectors in New York on June 4 and run right up to the gavel.

What makes the Sienna Star a headline is not just its size — though 73 carats of saturated, sun-soaked yellow is a spectacle in its own right. It is the color grade. Fancy Vivid Yellow is the single highest color designation the Gemological Institute of America awards to a yellow diamond, and a stone this large reaching that grade is the kind of pairing that happens perhaps once in a generation. Set by London designer Glenn Spiro, the stone sits at the heart of an 18-karat white-gold ring scattered with more than four carats of pavé diamonds on a flexible shank.

It headlines a sale already stacked with rarity — a 25.29-carat Kashmir sapphire by Bulgari, a Burmese ruby ring, and more than 168 carats of signed diamond jewels. But it is the Sienna Star, glowing the color of late-afternoon sunlight, that everyone is talking about.

The Sienna Star — 73.11 carats, Fancy Vivid Yellow, VS2 clarity, set by Glenn Spiro. One of the largest of its color ever to reach auction. Headlining Sotheby's New York Magnificent Jewels, June 9, 2026. (Sotheby's)

What the GIA Found: The Full Profile of the Sienna Star

According to its GIA report, the Sienna Star is a cut-cornered square step-cut diamond weighing 73.11 carats, graded Fancy Vivid Yellow with natural color origin and VS2 clarity. Fancy Vivid is the highest saturation grade on the GIA's colored-diamond scale — the point at which a yellow diamond stops looking pale or "Cape" and starts glowing like concentrated sunlight. A stone reaching that grade at this carat weight is exceptionally rare.

From "Cape" to Canary: Why Fancy Vivid Yellow Is a Class of Its Own

Yellow is the most familiar of the fancy diamond colors — but that familiarity hides how rare a truly vivid yellow actually is. The vast majority of yellowish diamonds are faint, "Cape," or commercial-grade tints that gemologists work hard to mask. Reaching the top of the scale is a different story entirely.

A yellow diamond gets its color from nitrogen trapped in the carbon lattice as the crystal forms. Trace nitrogen produces a pale tint; the rare concentration and arrangement that produces a deep, even, electric yellow is a geological lottery. The GIA grades yellow across a ladder — Fancy Light, Fancy, Fancy Intense, and finally Fancy Vivid, the most saturated grade of all. Only a small fraction of natural yellow diamonds ever earn the Vivid designation, and the proportion shrinks dramatically as size climbs.

That is what puts the Sienna Star in a category alone. A Fancy Vivid Yellow under five carats is already a special stone. A Fancy Vivid Yellow at 73 carats — holding even, saturated color across that much crystal with VS2 clarity — is the kind of combination that auction houses build an entire sale around. There is simply no commercial supply of stones like this; each one is a singular event.

Fancy Vivid Yellow is the highest saturation grade the GIA awards to a yellow diamond — and only a small fraction of natural yellows ever reach it.

Where the Sienna Star Sits in the Yellow Diamond Record Books

Big vivid yellows have a habit of rewriting price expectations whenever they appear. The Sienna Star arrives at a moment when colored gemstones and colored diamonds are among the fastest-appreciating categories in the entire jewelry market — and the headline names give a sense of just how high the ceiling goes.

The broader backdrop only sharpens the interest. Sotheby's has been posting record sell-through at its recent jewelry sales, and demand for colored stones and colored diamonds has surged as wealthy buyers increasingly treat exceptional gems as a store of value. Against rising gold prices and economic uncertainty, the appetite for one-of-a-kind natural color has rarely been stronger — exactly the climate in which a stone like the Sienna Star tends to surprise on the upside.

What the Sienna Star Tells Us About the Colored Diamond Market in 2026

One headline stone is also a market signal. The Sienna Star's arrival fits a pattern that has defined fine jewelry for the past several years: natural color is where the energy — and the money — is going.

Natural Colored Diamonds at Incline Village Since 1984

A $3 million headline diamond sits at the very top of a spectrum that runs all the way down into the cases of independent jewelers like Forever Rox Fine Jewelry. Natural fancy colored diamonds — yellow, pink, blue, green — appear at every price point, and the same rarity that drives the Sienna Star applies at every level of the market. A natural Fancy Vivid Yellow in a custom engagement ring carries a rarity a white diamond of the same size simply does not.

Forever Rox Fine Jewelry in Incline Village has worked with natural colored diamonds, custom colored-stone designs, and fine gemstone sourcing since 1984. If the Sienna Star has you thinking about natural color — whether for a custom engagement ring, an anniversary piece, or an investment-grade loose stone — the conversation starts at (775) 831-4544 or at foreverrox.com.

Common Questions About the Sienna Star Diamond