Sherlock Holmes had opened his mouth to reply, when the door flew open, and Peterson, the commissionaire, rushed into the apartment with flushed cheeks and the face of a man who is dazed with astonishment.
“The goose, Mr. Holmes! The goose, sir!” he gasped.
“Eh? What of it, then? Has it returned to life and flapped off through the kitchen window?” Holmes twisted himself round upon the sofa to get a fairer view of the man’s excited face.
“See here, sir! See what my wife found in its crop!” He held out his hand and displayed upon the centre of the palm a brilliantly scintillating blue stone, rather smaller than a bean in size, but of such purity and radiance that it twinkled like an electric point in the dark hollow of his hand.
Sherlock Holmes sat up with a whistle. “By Jove, Peterson!” said he, “this is treasure trove indeed. I suppose you know what you have got?”
“A diamond, sir? A precious stone. It cuts into glass as though it were putty.”
“It’s more than a precious stone. It is the precious stone.”
“Not the Countess of Morcar’s blue carbuncle!” I ejaculated.
— Arthur Conan Doyle, The Adventure of the Blue Carbuncle
I have always wondered what the titular stone really was in this Sherlock Homes story. Now I know that Conan Doyle was describing a blue garnet.
Do they really exist? Until the 1990s, no one thought so.
Chemistry is destiny
Garnets, whether natural or man-made, form under high heat and pressure. In nature, these harsh conditions, of course, produce a lot of industrial grade stones. Because garnet is hard – and, at Mohs 6.5-7.5, garnets certainly can cut glass – such stones are used for abrasive papers, in sandblasting, and in steel-cutting water jets.
Its electromagnetic properties also make synthetic garnet useful for specialized tasks like YAG lasering and in magnetic films.
Gem-quality stones have the same crystalline structure and physical properties as all members of the garnet group, but they’re transparent and come in every color of the rainbow (except, possibly, blue).
Down through the ages many different names have been given to members of the garnet family, but today geologists classify most garnets based on “X” and “Y” in the general formula: X3Y2(SiO4)3.
We’re after the uncommon, though – a blue garnet. None of the above fit the specs.
Pyropes (where “X” equals magnesium) are typically dark to ruby red, almandines (“X” usually equals iron) reddish brown to brown, and spessartines (“X” equals manganese) are orange, pink, or brown.
Uvarovites (“Y” equals chromium) are green; grossulars (again, “Y” equals aluminum) colorless, orange, or green; and andradites (“Y” equals iron) are brown, black, or green.
Chemistry certainly is destiny when it comes to color. Magnesium in a garnet makes the gem red, chromium turns it green, and iron often leads to brown or black.
How about titanium, the element that, together with iron, makes sapphires blue?
Yes, andradites sometimes have titanium in them, but it turns these garnet crystals a deep black color, which is why they’re called melanite.
Blue…we have blue!
In the Victorian era, there were bright violet almandines, but it wasn’t until the 1990s that blue garnets were found in Madagascar (PDF).
Gemologists studied the garnets and realized that the color came from an unusually high amount of vanadium. Since then, reportedly, blue garnet has also been found in parts of Africa, Russia, North America and Asia (Turkey).
Language and price
We’ve found the blue garnet! Now where does “carbuncle” come in?
Nowadays, that’s a medical term to describe a boil. The word itself, however, has also always been associated with red jewels. The Latin carbunculus means either “red gem” or “red inflamed spot.” Ironically, it is derived from the same root as “carbon,” which is not found in natural garnet (though anything’s possible these days).
The specific red jewel that “carbuncle” has referred to down through the centuries appears to have usually been almandine, the most common red garnet variety, sometimes called “precious garnet.”
A blue carbuncle, therefore, would have been a very valuable gem in Victorian times.
Today, as of the time of this writing, it’s valued at roughly USD 1000 per carat.
Why not a sapphire?
We haven’t yet found a blue almandine, but as garnets are made of a solid solution, and since almandine sits in the same chemical series as pyrope and spessartine, a blue carbuncle probably isn’t entirely out of the question.
There is no way that Sir Arthur Conan Doyle could have known this when the story was published, a century before the first blue garnet gem was found.
He most definitely was interested in geology. It is present, though not always accurately, in The Lost World, and his Sherlock Holmes stories actually inspired the real-world field of forensic geology.
But why did Conan Doyle pick a garnet for the stolen jewel in his story, and why did it have to be blue? A fabulous diamond or some other more traditional precious stone would have served the purpose very well.
We’ll never know for sure, but it’s interesting to note, that earlier in Conan Doyle’s career, when he was a ship’s doctor on a voyage to Portugal and West Africa in 1881, he had met Henry Highland Garnet, US consul to Liberia.
Conan Doyle was profoundly impressed with this former slave and prominent abolitionist.
Garnet died a year after Doyle met him. His influence has been invoked to explain the delightful twist at the end of another Homes story, “The Adventure of the Yellow Face,” which came out a year after “The Adventure of the Blue Carbuncle.”
When outlining the story that would become “The Adventure of the Blue Carbuncle,” perhaps Conan Doyle remembered Garnet and was also taken with the link between the color blue and the sea, not to mention the fact, accepted up until the 1990s and still found in USGS online information, that garnets could be any color but blue.
We’ll never know for sure. I’ll certainly never be able to read this excellent Sherlock Holmes story again without thinking of Henry Garnet. What a remarkable tribute to this man!
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- The Garnet Group of Minerals. Amethyst Galleries
- Garnet Jewelry. Collectors Weekly
- Garnets. Minerals.net
- All About Garnets. Chris Ralph
- Garnets From Madagascar With a Color Change From Blue-Green to Purple. Karl Schmetzer and Henz-Jurgen Bernhardt, Gemological Institute of America.
- Garnets. United States Geological Survey
- Garnet. Wikipedia