In its character yttrium is closely allied to, and in nature is always associated with, cerium, lanthanum, didymium and erbium (see Rare Earths).
Of yttria, Y203, and 42.75 of the oxides of erbium, cerium, didymium, lanthanum, iron, beryllium, calcium, magnesium and sodium.
ERBIUM (symbol, Er; atomic weight, 165-166), one of the metals of the rare earths.
Erbium forms rose-coloured salts and a rose-coloured oxide.
Meyer thinks that the susceptibilities of the metals praseodymium, neodymium, ytterbium, samarium, gadolinium, and erbium, when obtained in a pure form, will be found to equal or even exceed those of the well-known ferromagnetic metals.
Many of their compounds are very strongly magnetic, erbium, for example, in Er203 being four times as strong as iron in the familiar magnetite or lodestone, Fe203.
In the 4th century it is named by the poet Ausonius in his Ordo nobilium erbium, chiefly, perhaps, on the strength of its historic memories.