The Black Prince's Ruby
A large red spinel, long called a ruby, set in the Imperial State Crown of England at the Tower of London, which Wikipedia's list of allegedly cursed objects says brings misfortune to its owners.
The Gemological Institute of America treats the stone as one of the best-known spinels. It says the gem is crimson-red, polished and roughly octagonal, probably came from the mountains of Afghanistan, and first appears in records from fourteenth-century Spain. According to GIA a series of Spanish and Moorish kings owned it before it went, in 1367, to Edward, Prince of Wales, called the Black Prince, in payment for winning a battle. It is now set in the Imperial State Crown and shown at the Tower of London.
Wikipedia is more cautious. It says the story that Peter of Castile gave it to the Black Prince in 1367 is a legend that dates from the 1760s. It adds, with a citation-needed tag, that Henry V is said to have worn the stone at Agincourt in 1415, and it places the mine in Badakhshan. Its account of how Don Pedro got the stone is violent: he had the servants of Abū Sa'īd killed, may have stabbed Abū Sa'īd himself, and took the spinel from the dead man's body. Wikipedia marks that passage as failing verification.
The curse has one source here. Wikipedia's list of allegedly cursed objects says the stone is said to cause misfortune and early death for its owners. GIA's history of the stone and Wikipedia's own article on it, as excerpted here, say nothing of a curse.
"According to a legend originating from the 1760s, the stone has been in the possession of the English and later British monarchy since it was given in 1367 by the Spanish king Peter of Castile to the Prince of Wales, Edward of Woodstock, known as the "Black Prince".[2] Henry V is said to have worn it at the Battle of Agincourt in 1415.[citation needed] The stone is believed to have been mined in Badakhshan in present-day Afghanistan,[3] the principal source of large spinel gems in the Middle Ages."
- Spinel History and Lore, Gemological Institute of America (GIA)
- Black Prince's Ruby (Don Pedro of Seville), Wikipedia
- King Henry VIII's Jewel Book (1521), ed. Edward Trollope, Associated Architectural Societies Reports and Papers vol. 17, Associated Architectural Societies (1884); Internet Archive scan
- List of allegedly cursed objects, Wikipedia