Steel gray metal which gives a deep blue color to glass (Cobalt Blue Glass). m.p. 1495 ºC; 2723 ºF b.p. 2870 ºC; 5198 ºF density 8.9 g/cc; 555.6 pound/cubic foot	memory peg
	c. 1735 Georg Brandt, Germany
	Kobold = evil spirit (German)

The word Cobalt derived from the German "kobold" = a goblin, gnome, evil spirit (> Mittelhochdeutsch "kobe" [hut, shed] + "holt" [goblin, from "hold" = gracious, friendly; complimentary words used to avoid the wrath of troublesome beings — for another derivation, see bottom of page]).
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.

Christoph Schürer of Platten, Bohemia, about the middle of the sixteenth century found that this kobald coloured glass and pottery more intensely blue than copper. Low grade kobald could be used for bluing to counteract natural yellowing of laundry. However, the colouring properties of the ore has been known since very ancient times. There was even one piece of cobalt blue glass in Tut-Ankh-Amen's tomb in Egypt.
In 1735, Georg Brandt (1694-1768) pointed out that the primary cause to the blue color of those glass and smalts was due to the presence of a metal or semi-metal, that he called cobalt rex. About 1741 he wrote:

"As there are six kinds of metals, so I have also shown with reliable experiments... that there are also six kinds of half-metals: a new half-metal, namely Cobalt regulus in addition to Mercury, Bismuth, Zinc, and the reguluses of Antimony and Arsenic."

Some think the name is derived from the Greek [kobalos] = mine.
An etymological website gives the following explanation for the etymology of the word goblin: "Standard scholarship holds that English took goblin from the French gobelin. The problem with this is that, while Middle English had the word goblin as early as 1320, there is no record of the French word gobelin until the 16th century. Interestingly, a 12th century cleric called Ordericus Vitalis mentions Gobelinus as the name of a spirit which haunted the neighbourhood of Évreux. It is possible that gobelin evolved from the ancient Greek kobalos «rogue, knave», via the Medieval Latin cobalus. If so, it is related to the German kobold, and hence to the name of the metal cobalt."
The word kobalos is not in my Greek dictionary.

• In the 19th century a native Czech name was proposed: dasík, maybe from "des" = terror.

• Mary Elvira Weeks, Discovery of the Elements, comp. rev. by Heny M. Leicester (Easton, Pa.: Journal of Chemical Education, 1968), pp. 148-157.
• Die Erfindung des Kobaltblau (in German, about Christoph Schürer).