Decipium was the proposed name for a new chemical element isolated by

Marc Delafontaine Marc Delafontaine (March 31, 1837/1838, Céligny, Switzerland–1911) was a Switzerland, Swiss chemist and spectroscopist who was involved in discovering and investigating some of the rare earth elements. Career Delafontaine studied with Jean C ...

from the mineral

samarskite Samarskite is a radioactive rare earth mineral series which includes samarskite-(Y), with the chemical formula and samarskite-(Yb), with the chemical formula . The formula for samarskite-(Y) is also given as . Samarskite crystallizes in the ort ...

. He published his discovery in 1878 and later published a follow-up paper in 1881. Decipium was considered to be in the cerium group of rare earths.

Harmsworth's Universal Encyclopaedia ''Harmsworth's Universal Encyclopaedia'' is an encyclopedia edited by John Hammerton and published in London London is the Capital city, capital and List of urban areas in the United Kingdom, largest city of both England and the United ...

vol X, 1922 p6493 Rare Earths. In 1880, spectral analysis proved that decipium had a high

samarium Samarium is a chemical element; it has symbol Sm and atomic number 62. It is a moderately hard silvery metal that slowly oxidizes in air. Being a typical member of the lanthanide series, samarium usually has the oxidation state +3. Compounds of s ...

content. It is now believed that Delafontaine's decipium sample was a mixture of

with traces of other

rare earth elements The rare-earth elements (REE), also called the rare-earth metals or rare earths, and sometimes the lanthanides or lanthanoids (although scandium and yttrium, which do not belong to this series, are usually included as rare earths), are a set of ...

References

Misidentified chemical elements Samarium 1878 in science {{chem-hist-stub