Carbuncle

The Carbuncle, Chapter 18: Copper, Broken Mirrors, Rooster Feathers, Uncut Ruby

From Borges-
"In mineralory the carbuncle, from the Latin carbunculus, "a little coal" is a ruby; as to the carbuncle of the ancients, it is supposed to have been a garnet.
In sixteenth-century South America, the name was given by the Spanish conquistadors to a mysterious animal- mysterious because no one ever saw it well enough to know whether it was a bird or a mammal, whether is had feathers or fur. The poet-priest Martin del barco Centenera, who claims to have seen it in Paraguay, describes it in his Argentina only as "a smallish animal, with a shining mirror on its head, like a glowing coal...."...."