Periodic Table--Neodymium

Neodymium is a rare earth element (REE) that occurs in many silicate, phosphate, and carbonate minerals by substitution for major ions. It has seven stable isotopes. Nd and samarium (Sm) are considered "light" REEs and become concentrated in feldspars, biotite, and apatite. The concentrations of Nd and Sm increase in minerals during sequential crystallization, but the Sm/Nd ratio decreases.

¹⁴⁷Sm decays by alpha emission to stable ¹⁴³Nd, with a half-life of 1.53 x 10¹¹ years. Variations in Nd isotopic compositions (¹⁴³Nd/¹⁴⁴Nd) are the result of elemental fractionations occurring between ¹⁴³Nd and its parent ¹⁴⁷Sm during radioactive decay. This has made Nd useful for age dating terrestrial and extraterrestrial materials as well as many other geologic applications (DePaolo, 1988). The growth of ⁸⁷Sr and ¹⁴³Nd together provides useful insight into geochemical evolution. Mafic rocks and associated suites of more differentiated rocks can be dated by whole-rock or internal mineral isochrons. These Sm-Nd dates are less susceptible to metamorphic alteration than Rb-Sr dates.

The concentration of Nd in natural waters is extremely low because the natural abundance of Nd is very small, and Nd is non-hydrophilic in low temperature environments. In most geological environments, the isotopic composition of Nd varies systematically, though inversely, with the isotopic composition of Sr. Except in very specific environments, Nd will not be as useful as Sr (due to its higher concentration in natural waters) in the interpretation of the weathering process in rocks and minerals. And because of their similar geochemical behavior, Sm and Nd are not fractionated from one another as severely as Rb and Sr. This fact, combined with the very long half-life of ¹⁴⁷Sm make variations in Nd isotopes useful in only very old environments.

Source of text: This review was assembled by Eric Caldwell and Dan Snyder from Nimz (1998), and from the references below.