Whither Promethium: Has the Traditional REE Plot Become an Anachronism?

Current common usage of chondrite-normalized rare earth element (REE) plots has seen the advent of the disappearance of promethium as a regular phenomenon, in addition to the occasional omission of other analytically compromised lanthanides, and the substitution of Y for similarly sized heavy lanthanides. This communication represents an examination of the underlying principles behind the normalized lanthanide plot, the reasons for increased flexibility in the application of the plot, and recommendations for its use. Specifically, the distinction between the lanthanides and the rare earth elements sensu lato, and the resultant distinction between normalized lanthanides plotted according to their atomic number and REE (or other REE-incorporating) spidergram plots, is highlighted. The distinction is made between the traditional REE plot and what should arguably be described as a modified REE spidergram, which can accommodate chemical interventions. The current actual role of induced Pm as an industrial element is also noted as a justification for the continued recognition of its existence.