Decipium was the proposed name for a new chemical element isolated by Marc Delafontaine from the mineral samarskite. 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 vol X, 1922 p6493 Rare Earths.
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.
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