Geoff Lander: O Rare New Earths

Why should a student of chemical history
visit the pit at the Swedish town Ytterby?
Eggheads will proffer, for periodicity.
Shame on the chemists who parroted, Y?

Clue? A soliloquy? Tb or not Tb?
Hellish abstruse? Not at all, elementary.

Ytterby's waste was the cause of the mystery.
Spoil, with chemistry fitting no category,
save for its bally inseparability!
Shame on you students who parroted, Y?

Sever a letter, and heigh ho! – Ytterbium;
pare down for Yttrium, Terbium, Erbium;
enter two others: (Stock)Holmium, Thulium,
few of which rarities feature at schoolium.