Decipium was the proposed name for a new chemical element isolated by Marc Delafontaine from the mineral samarskite.
[1][2][3] Decipium was considered to be in the cerium group of rare earths.
[4] In 1880, spectral analysis proved that decipium had a high samarium content.
It is now believed that Delafontaine's decipium sample was a mixture of samarium with traces of other rare earth elements.
This history of chemistry article is a stub.