School of Engineering and Science - Jacobs University

4
Ce
valency
3
Sc
Lu
Y
La
Eu
2
0.8 0.9 1.0 1.1 1.2 1.3
ionic radius (Å)
Figure 2. Valence state and ionic radius (coordination number 8) for rare earth elements. Yttrium has an
ionic radius that falls between Dy and Ho. Cerium and Eu are the only rare earth elements that exist at
valence states other than +3 (ionic radii data from Shannon, 1976).
Rare earth element data are typically normalized for plotting, as REY
concentrations may vary by an order of magnitude (or more) between adjacent elements
in the series, due to the greater abundance of elements with even atomic numbers
relative to elements with odd atomic numbers (Oddo-Harkins rule). Figure 3 shows data
for mid-ocean ridge basalt (MORB) that has been normalized to C1 chondritic meteorite
(Anders and Grevesse, 1989), as well as non-normalized data for comparison, and
where Y has been inserted between Dy and Ho according to its ionic radius (see Figure
2). If none of the REY exhibit anomalous behavior then the normalized REY pattern
will vary smoothly across the series as seen in Figure 3. It should be noted that the C1
chondritic meteorite is often used for normalizing REY data, as it is considered to
possess a REY distribution equivalent to bulk silicate Earth. However, it is sometimes
useful to normalize REY data to other geochemical reservoirs, and another commonly
used REY dataset for normalization purposes (and one used extensively in this thesis) is
upper continental crust, as represented by the Post Archean Average Shale (PAAS) of
McLennan (1989).
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