I knew that the word magnet was ultimately from Greek Magnētis (lithos) ‘Magnesian (stone),’ which the AHD says is “from Magnēsiā Magnesia, an ancient city of Asia Minor.” Merriam-Webster’s concurs: “stone of Magnesia, ancient city in Asia Minor.” But my problem, as I looked at my map of Asia Minor, was that there were two Magnesias: Magnesia ad Maeandrum (‘on the Meander River’), now in ruins, and Magnesia ad Sipylum (‘at the foot of Mt. Sipylus’) or ad Hermum (‘on the Hermus River’), now buried beneath the Turkish city of Manisa (whose name obviously derives from it). So I did some googling to try to find out which Magnesia we were talking about, and what did I find but my old friend, the Elementymology & Elements Multidict by Peter van der Krogt, whose magnesium entry says:
The names magnesia alba and magnesia nigra are derived from Magnesia, Μαγνησια, a prefecture in Thessaly (Greece)… Manganese and Magnesium were abundant in oxide and carbonate ores in this region, and they therefore became referred as Μαγνητις λιθος, or stones from Magnesia. The region also contained large amounts of iron oxides (magnetite, or lodestone, for example) so that the ores were magnetized. That explains why magnesium as well as magnet (and magnetism) are derived from Magnesia, while magnesium is not magnetic.
(Emphasis added.) He certainly sounds like he knows what he’s talking about… but could my two favorite American dictionaries both get it wrong? The OED records an ancient dispute and takes no sides:
The origin of the Greek terms is uncertain, and was disputed in antiquity. They may refer to an origin in the district of Magnesia in the east of Thessaly (cf. MAGNESIAN n. and a.1), or in the territory of the city Magnesia ad Sipylum in Lydia; on the other hand, Pliny (Nat. Hist. 20. 2; 36. 126-7) cites Nicander as his authority for the derivation from the name of a shepherd, Magnes, who found that the ground on Mount Ida attracted the iron nails in his shoes and the ferrule of his staff.
Does anybody know if this can be pinned down once and for all?
Update (Dec. 28, 2011). The new Fifth Edition of the AHD has added Thessaly as a possibility: “after Magnēsiā, a region of Thessaly, or Magnēsiā, a city in ancient Lydia.” Good for them!