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. In 1880 spectral analysis proved that decipium had a high samarium content. It is now believed that Delafontaines decipium sample was a mixture of samarium with traces of other rare earth elements. References Misidentified chemical elements Samarium 1878 in science