Cobalt in modern English is first a chemical element: a hard, magnetic, steel-grey metal, symbol Co, atomic number 27, found with nickel and copper ores and used in high-temperature alloys, rechargeable batteries, and blue pigments. By a later shift it is also the colour itself, the intense blue of glass and paint. The origin of the word cobalt does not start in a laboratory. It starts as a German miners’ name for a rock they wished they had never struck.
A borrowing from the mine, not from Latin
English took the noun in the late 1600s from German Kobalt, also spelled Kobald, Kobolt, and similar forms. That German word is the same as Kobold, a household or mountain goblin. In learned lists the initial letter was pulled toward Latin cobaltum, which is why English writes cobalt with a c. The substance was not inherited from Old English; it is a straightforward borrowing.
The mining sense is older than the English one. In the sixteenth century Johannes Mathesius writes Cobalt for a mineral Saxon miners treated as trash, and Paracelsus has Kobolt. German historical dictionaries treat these as Upper Saxon forms of Kobold, used first as an insult, in the same vein as later miner names such as Nickel and Wolfram. The setting is the silver country of the Harz and neighbouring districts. The ore looked as if it should give copper or silver. It did not. Mixed with arsenic and sulphur, it spoiled the smelt and threw off fumes that made crews ill. Miners said a mountain spirit had stolen the real metal and left this substitute. Another account of the nickname is more workaday: the rock resembled copper and then yielded none, a kind of mineral fool’s gold.
English later borrowed kobold itself for the sprite. Cobalt and kobold are therefore doublets from one German word: one track kept the goblin, the other kept the metal.
The older German compound
Kobold is generally treated as a Middle High German compound, already visible in the thirteenth century as a house spirit, sometimes helpful, sometimes treacherous. The first element matches kobe, a hut, shed, or stall. The second element is disputed. One reconstruction posits a goblin piece *holt, from hold, meaning gracious or friendly, a polite label for a being you would rather not provoke. Another ties the second half to walten, to rule or to keep watch, so the whole would mean a house-guardian. Later German work has tried to attach the name to St Nicholas and winter customs; Jacob Grimm looked toward water-sprites. None of those deeper links is settled. Early German uses can even mean a fool or a contemptible person rather than a supernatural creature. For the metal, the important fact is narrower: by the 1500s, miners already heard a trickster in that grey rock.
In English, cobalt has no prefix or suffix that speakers still feel. Chemical English later built cobaltic and cobaltous for salts in different oxidation states. Those are laboratory additions, not part of the original loan.
Ore, blue glass, then an element
The word pointed at the ore long before chemists agreed that a new metal sat inside it. Glassmakers had already learned, in the sixteenth century, that cobalt-bearing minerals would stain glass a deep blue; the pigment trade later called that preparation smalt. The colouring power is older still in material history: cobalt minerals tinted glass in Egypt and Mesopotamia. That is the history of a pigment, not of the English name. The name is German, and it spread in German as the blue use became commercial in the seventeenth century.
In the 1730s the Swedish chemist Georg Brandt showed that the blue in such ores did not come from bismuth, which often occurs in the same veins. He argued for a distinct metal and kept the miners’ word. Handbooks disagree about the exact year. Some credit 1733; many say about 1735; his account sat in a Swedish learned journal whose volume covering 1735–1739 was issued in 1739; a few sources place a cleaner isolation in the early 1740s. Other chemists for a time claimed his metal was only iron and arsenic. The chronology is fuzzy. The naming choice is not: Brandt did not invent a Greco-Latin root. He promoted the cursed ore’s nickname into the language of elements.
English already had cobalt for the steel-grey metal by the 1680s, so Brandt was confirming a substance whose German name had already crossed the Channel. The colour sense in English, cobalt as a blue, is recorded in the 1830s.
A parallel sits one place over on the periodic table. German Kupfernickel, roughly copper-goblin or false copper, gave English nickel: another ore that looked useful and then refused. Cobalt and nickel still travel together in the ground, which is why the folklore and the chemistry do too. French cobalt, Dutch kobalt, Swedish kobolt, and the Romance forms cobalto are the same German loan moving through scientific European vocabularies.
A leftover goblin
The modern metal is a battery ingredient and a magnet alloy. The headword does not mention any of that. What it still carries is the miners’ complaint: a rock that impersonated a prize and then poisoned the furnace. The fossil in the spelling is the goblin, not the laboratory.