The rarest of the naturally-occurring rare-earth metals, thulium was discovered in 1879 by Cleve, working from samples of erbia, an oxide of erbium. The metal is named for the ancient name for Scandinavia, Thule.
Like others in the lanthanide series, thulium is silver in color but it is also very soft---soft enough to cut with a knife.
Contributors and Attributions
Stephen R. Marsden