Miners were puzzled at some varieties of copper ore which didn't yield copper when smelted, and suspected foul play from kobolds, a type of mythical sprite. Upon closer examination, it was a new element (after Phosphorus), and Brandt named it cobalt. This was the first metal to be discovered not known to the medeival alchemists.
A visual chronology of Asimov's ~1500 scientific inventions and discoveries.
