Comment Re:Lithium isn't rare, and it is important (Score 3, Informative) 51
Isaac Asimov explained it this way:
Using modern terminology, we would define an earth as a stable oxide with a high melting point. The four most common of these were silica, alumina, lime and magnesia, in that order....
In 1812, a Scottish chemist, Thomas Thomson (1773-1852), visited the [Ytterby] quarry and marveled over the mineral [ytterbite]. He was still under the spell of the word “earth.”
If an object was called an earth, surely it would have to be a major component of the earth....
Now Thomson was staring at an earth, yttria, that could only be found in one or two favored spots and was unknown elsewhere....
Yttria, in other words, was a “rare earth” which, to Thomson, was almost a contradiction in terms, and that very contradiction helped make the phrase notable to chemists, generally.
