Here's the story about the nickel ore. Note that the metal cobalt was named for kobolds as well.http://elements.vanderkrogt.net/elem/ni.html
Saxon miners were familiar with the reddish-coloured ore, a combination of arsenic and nickel (niccolite, NiAs), which superficially resembles Cu2O. These miners attributed their inability to extract copper from this source to the work of the devil and named the ore Kupfernickel (in Swedish kopparnickel). Originally it was a term of abuse used by the miners in the Erzgebirge (Ore Mountains), who searching for Silver found this "inferior" metal. The word is derived from Kupfer = Copper and Nickel = demon, goblin, rascal (a pet form of the name Nikolaus [Nicholas], hence Old Nick "the devil"). Thus kupfernickel - Latinized as Cuprum Nicolai - can be translated as "old Nick's Copper" (or "Devil's Copper").http://elements.vanderkrogt.net/elem/co.html
In some mining regions there were specific prayers to protect the miners from those kobolds, who by German superstition were delighted in destroying the work of miners, causing them endless trouble. The word then became also the term silver miners used for worthless rock, laced with Arsenic and Sulphur (cobaltite, CoAsS).
Paracelsus (Theophrastus Bombastus von Hohenheim, 1493-1541) vaguely mentioned cobalt in his Book of Minerals as a troublesome and worthless mineral found in large quantity in mines on the borders of Saxony and Bohemia. Miners disliked it because of the labor of removing it and because it often accompanied Arsenic which imperiled their health. The term cobalt was also used by Basilius Valentinus (14th century) and Georgius Agricola (1494-1555), to denote substances which, although resembling metallic ores, gave no metal on smelting