Carbuncle was a mythical creature reportedly sighted in the Americas by Spanish conquistadors. It is described as a small creature, either a bird or a mammal, that has a gem in its forehead crystallized from the brain of a dead dragon. According to myth, it is good luck to catch a carbuncle. A carbuncle is also an archaic name given to any red cabochon cut gemstone. The name applied particularly to red garnet.