Ytterbium is a lanthanide series, rare earth element denoted by the atomic symbol, Yb. It has an atomic number of ytterbium is 70 and its atomic weight is 173.04. The element is a bright, silvery metal with a melting point of 1,506.2°F (819°C) and a boiling point of 2,184.8°F (1,196°C). It is soft, ductile, and malleable.

In 1878, Jean-Charles Galissard de Marignac (1817-189) analyzed a rare earth material known as erbia and found that it consisted of two parts. He retained the name erbia for one part and called the other part ytterbia. A year later, the Swedish chemist, Lars Fredrik Nilson, showed that ytterbia itself is a mixture of two oxides, which he called scandia and ytterbia. Nilson is acknowledged as the discoverer of the element scandium and, sometimes, of the element ytterbium.

Other authorities reserve credit for the discovery of the latter element, however, for the French chemist Georges Urbain (1872-1938). Urbain showed in 1907 that Nilson's ytterbia was actually a mixture itself of two oxides. The first he named lutecia and the second, neoytterbium, in order, he said, "to leave the illustrious Marignac, in the future, the credit of his fundamental discovery." The name of the second element was eventually shortened, however, to ytterbium. Ytterbium is identical to cassiopeium, discovered at about the same time by Auer von Welsbach (1858-1929).

Ytterbium is found naturally in monazite sand. It makes up about 0.03% of this mineral. It can be isolated by ion-exchange or solvent extraction techniques. Few applications for this material have been found. It has been suggested that could be added to improve the strength characteristics of stainless steel.