Quick answer: the most famous gemstones in the world include the Hope Diamond, the Cullinan, the Koh-i-Noor, the Star of India, the Logan Sapphire, the Tiffany Yellow Diamond, the Black Prince’s Ruby, and the Timur Ruby. The twist: those last two “rubies,” among the most celebrated red gems in history, are not rubies at all. They are spinel.
1. The Hope Diamond
A 45.52-carat deep blue diamond, now at the Smithsonian in Washington, D.C. Its trail runs through French royalty and a long line of owners, many of whom had famously bad luck, which fed a “curse” legend that sellers were happy to promote. In 1958 jeweler Harry Winston donated it to the Smithsonian and sent it through the U.S. mail in a plain package. Its scientific party trick: after exposure to ultraviolet light, it glows an eerie red-orange for several seconds, thanks to its boron content. More on that in why some rocks glow under UV.
2. The Cullinan
The largest gem-quality rough diamond ever found, at 3,106 carats (over a pound and a half), discovered at the Premier Mine in South Africa in 1905. It was cut into nine major stones and around a hundred smaller ones. The largest, Cullinan I or the Great Star of Africa (530.2 carats), sits in the British Sovereign’s Sceptre with Cross.
3. The Koh-i-Noor
The “Mountain of Light” has passed through Mughal, Persian, Afghan, and Sikh rulers before ending up in the British Crown Jewels. It was recut in 1852 to 105.6 carats, which disappointed many people at the time because it lost a large share of its weight. Its ownership is still politically contested, with claims from India, Pakistan, and others.
4. The Star of India
A 563-carat star sapphire at the American Museum of Natural History in New York, and one of the largest of its kind. A six-rayed star glides across its dome, an effect called asterism, caused by needle-like inclusions of rutile aligned in three directions (see Chatoyancy and Asterism). In 1964 it was stolen in a famous jewel heist by Jack “Murph the Surf” Murphy and his accomplices, who climbed in through a window left open for ventilation. It was recovered months later in a bus station locker in Miami.
5. The Logan Sapphire
A 422.99-carat cornflower-blue sapphire from Sri Lanka, also at the Smithsonian, and one of the largest faceted blue sapphires on display anywhere.
6. The Tiffany Yellow Diamond
Found in South Africa’s Kimberley mines in 1877 and cut to 128.54 carats, this canary-yellow diamond has been worn publicly by only a handful of people. Its yellow comes from nitrogen atoms in the carbon lattice.
7 and 8. The Black Prince’s Ruby and the Timur Ruby: actually spinel
The Black Prince’s Ruby is a large red stone, about 170 carats, set at the front of Britain’s Imperial State Crown, directly above the Cullinan II. Legend says it belonged to Edward of Woodstock, the Black Prince, in the 1360s, and that Henry V wore it in his helmet at the Battle of Agincourt in 1415. The Timur Ruby, about 352 carats, is engraved with the names of several of its former owners, including Mughal emperors.
Both are red spinel. For most of history, any fine red stone was called a ruby (or a “balas ruby,” or a “carbuncle”). Spinel and ruby look alike, form in similar rocks, and are often found together in the same gem gravels. But they are different minerals: ruby is aluminum oxide (corundum), while spinel is magnesium aluminum oxide with a different crystal structure. Spinel was only formally separated from ruby as its own mineral in the late 1700s, long after these stones had earned their names.
Today, fine red spinel is a prized gem in its own right, and arguably one of the best values in colored stones.
Misnomers are everywhere
Gem history is full of names that outlived the science. “Herkimer diamonds” are quartz, not diamond, named for their natural brilliance and double points. Our history of Herkimer diamonds covers how the name stuck, and pieces like our Large Double-Terminated Herkimer Diamond Quartz — Fort Plain, New York and Black Herkimer Diamond — Natural Smoky Point on Stand show why: they come out of the rock already faceted by nature.
The lesson famous stones keep teaching is the same: a name is a story; the mineral is a fact. When in doubt, ask what the stone actually is.
