Gray-white metal m.p. 1356 ºC; 2473 ºF b.p. 3123 ºC; 5653 ºF density 8.229 g/cc; 513.72 pound/cubic foot	memory peg
	1843 Carl Gustav Mosander, Sweden
	Ytterby, village in Sweden (just as Erbium, Yttrium, and Ytterbium!)

The story of Terbium is part of the story of the rare earth elements, which starts with Yttrium. After his discovery of Didymium (1842, see Praseodymium). Carl Gustav Mosander (1797-1858) turned his attention to yttria. In autumn of 1842 he was sure that yttria contained other rare earths as Theodor Scheerer had suggested. In Berzelius's Annual Report for 1842, published in April 1843, the discovery was announced. This was also published in an annex dated July 1843 to the German translation of his paper on the metals he found in Cerium: "Ueber die das Cerium begleitenden neuen Metalle Lanthanium und Didymium, so wie über die mit der Yttererde vorkommenden neuen Metalle Erbium und Terbium" (On the new metals Lanthanum and Didymium, accompanying Cerium, and on the metals Erbium and Terbium occuring with yttria) (note):

Mosander has separated yttria into three earths, a colorless oxide which kept the name yttria; a yellow earth erbia, and a rosy earth terbia, containing the elements Yttrium, Terbium, and Erbium. Was it lack of phantasy? All three names were derived from the Ytterby quarry where the gadolinite was originally found in 1787. It is also said that since the original earth was divided into three new earths, Mosander split the name of Ytterby in three parts: ytt, terb, and erb.

Berlin (1860) denied the existence of Mosander’s erbia, and gave this name to terbia. Delafontaine (1864, 1878) followed him in this, but proved also that the original erbia existed, and gave this now the name terbia, thus:

color of oxyde	Mosander 1842	Delafontaine 1864, 1878	element
colorless	yttria	yttria	Yttrium
yellow	erbia	terbia	Terbium
rose	terbia	erbia	Erbium

A new phase in the discovery of the rare earth elements started in the 1870s with the analysis of samarskite, found in Russia and in the United States (cf. Samarium). In 1878 the American chemist J. Lawrence Smith (1818-1883), researching samarskite found in North-Carolina, announced a new element, which he named Mosandrum, honouring the Swedish chemist Carl Gustav Mosander (note). Later was proved that it was impure terbia.

Mosander's original erbia was confirmed by Marc Delafontaine in 1878 and, renamed terbia, since the name erbia was already common for Mosander's terbia. Delafontaine illustrates his article with the following table, which should bring some clearness in the complicated matter of the rare earths (note):

Delafontaine's terbia was split by Marignac in 1886 into gadolinia and true terbia, which contained the present-day element Terbium.

The story is not ended yet. The unclear determination of the atomic weight (in the period 1864-1905 nine values were obtained, from 113 to 163,1), and by difficulties in interpreting the absorption spectrum. Lecoq described in 1886 the elements Zα and Zβ, the latter identical with Terbium (note), and Demarçay described imaginary elements like Ionium, Incognitium and Γ.

John and Gordon Marks suggested in 1994 the name Norium (No), together with Suevium (=Dysprosium) after Norway and Sweden where the lanthanides were discovered. 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).

Information and illustrations of Ytterby's quarry and a location map is on the Ytterbium page (see also Erbium and Yttrium).

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).