Reflective gray metal which forms a dark oxide with a slightly pinkish hue m.p. 1021 ºC; 1870 ºF b.p. 3068 ºC; 5554 ºF density (depending on allotropic form) 6.80 and 7.007 g/cc; 424.51 and 437.433 pound/cubic foot	memory peg
	1885 Carl Auer von Welsbach, Austria
	νεος + διδυμος (neos + didymos) = new + twins (Greek), new element found in Didymium

As described at Praseodymium Carl Gustav Mosander had named in 1842 a new element Didymium, from the Greek διδυμος (didymos) = twins), because it closely resembled Lanthanum and had been discovered in conjunction with it. Friedrich Wöhler objected this name and thought it had been given because Mosander had four children, all born as twins. Despite this, the name Didymium was in used for over 40 years.

A number of chemists believed that Didymium was a mixture of elements and in 1879 François Lecoq de Boisbaudran showed that it contained Samarium. In 1885 the Austrian chemist Carl Auer von Welsbach (1858—1929) separated the residual Didymium after removal of Samarium, into two elements (note): Neodymium (new twin) and Praseodymium (green twin), so retaining a part of the original name, with a new suffix. Neodymium forms the chief portion of the old Didymium and got the suffix νεος [neos] = new, young (thus in fact "new didymium"). Praseodymium gots its new name because of the green oxyde.

John and Gordon Marks suggested in 1994 the name Tyrium (Ty), after Tyr, in the Norse mythology god of war and strife and son of Odin (cf. uranium after Uranus) and for its tyrian (purple) coloured salts. The Marks brothers found the old names ugly and confusing. They offered alternative names that are equivalent contemporary (at the time and place of discovery) metaphors, both more euphonious and more memorable (note).

See also: Chronological list of discovery of the rare earths, their names in different languages etc. on the Yttrium page

Further reading:

• Mary Elvira Weeks, Discovery of the Elements, comp. rev. by Heny M. Leicester (Easton, Pa.: Journal of Chemical Education, 1968), pp. 667-699.
• Seltene Erden. Gmelins Handbuch der anorganische Chemie, 8. Aufl.; System-Nummer 39 (1938).
• Lauri Niinistö, Swedish Contributions to the Discovery of Elements: Part 3: The Work of Mosander, Cleve and Nilson. ERES Newsletter, vol. 12, no. 1 (30 June 2001). (on-line).
• Robert Plohn, "Seltene Erden". Zeitschrift 'Die Koralle', Sept. 1929 (on-line).