Carbuncle, originally spelt "Carbunkel" is a term given to a mythical beast reportedly sighted in the Americas by early Spanish conquistadors.
Although no firm eyewitness accounts are available, they have been described as small creatures, either birds or mammals. It is certain that they wear gems on their foreheads; such gems come from the brains of dragons.
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According to myth, dragons have inside their brain a liquid that crystallizes into a solid gem when they die. The legend of the jewel grew up around the Carbuncle creature and many men have supposedly searched for it, hoping to find the precious stone, without success.
It is mentioned in the Book of Imaginary Beings.