User:Georgiapeach5/Cerium anomaly

This is the sandbox page where you will draft your initial Wikipedia contribution.

If you're starting a new article, you can develop it here until it's ready to go live.

If you're working on improvements to an existing article, copy only one section at a time of the article to this sandbox to work on, and be sure to use an edit summary linking to the article you copied from. Do not copy over the entire article. You can find additional instructions here.

Remember to save your work regularly using the "Publish page" button. (It just means 'save'; it will still be in the sandbox.) You can add bold formatting to your additions to differentiate them from existing content.

Bibliography sandbox

The cerium anomaly, in geochemistry, is the phenomenon whereby cerium (Ce) concentration is either depleted or enriched in a rock relative to the other rare-earth elements (REEs)^[1]. A Ce anomaly is said to be "negative" if Ce is depleted relative to the other REEs and is said to be "positive" if Ce is enriched relative to the other REEs^[1].

Cerium Oxidation States

Cerium is a rare-earth element (lanthanide) characterized by two different redox states: III and IV. Unlike other lanthanide elements, which are only trivalent (with the notable exception of Eu²⁺), Ce³⁺ can be oxidized by atmospheric oxygen (O₂) to Ce⁴⁺ under alkaline conditions^[2].

The cerium anomaly relates to the decrease in solubility, which accompanies the oxidation of Ce(III) to Ce(IV). Under reducing conditions, Ce³⁺ is relatively soluble, while under oxidizing conditions CeO₂ precipitates^[1]. Sediments deposited under oxic or anoxic conditions can preserve the geochemical signature of Ce³⁺ or Ce⁴⁺ as long as no early diagenesis occurs^[1].

Crystal structure of Ceria-zirconia. Ce⁴⁺ has the same charge and similar ionic radius as Zr⁴⁺ resulting in elemental substitution and therefore a positive cerium anomaly.^[1]

Cerium Anomalies in Zircon

Zircon (ZrSiO₄) is commonly found in felsic igneous rock^[3]. Because both Ce³⁺ and Ce⁴⁺ can substitute for Zirconium, Zircon often has a positive Ce anomaly. Ce⁴⁺ substitutes with Zr much more easily than Ce³⁺ because Ce⁴⁺ (ionic radius 0.97Å) has the same charge and a similar ionic radius as Zr⁴⁺ (ionic radius 0.84Å)^[1]. Therefore, the oxidation state of the magma is what determines the Ce anomaly in Zircon^[3]. If the oxygen fugacity is high, more Ce³⁺ will oxidize to Ce⁴⁺ and create a larger positive Ce anomaly in the zircon structure. At lower levels of oxygen fugacity, the level of Ce anomaly will also be lower^[3].

Cerium Anomalies in Coal

Negative Cerium Anomalies

Cerium in coal is typically weakly negative, meaning that it is present at slightly lower concentrations than the other rare-earth elements^[2]. Cerium anomalies in coal are influenced by the sediment source region^[2]. Coal mined from mafic regions dominated by basalts, such as the location of the Xinde Mine in China, does not have a Ce-anomaly^[2]. In contrast, coal mined in felsic rock regions, such as Guxu Coalfield in in China, does have weakly negative Ce-anomalies^[2]. Negative Ce-anomalies can also be attributed to the weathering and oxidation of the coal-mining region^[1]. During oxidation, Ce³⁺ precipitates out as CeO₂, leaving less Ce in the coal^[2].

Positive Cerium Anomalies

While cerium anomalies in coal are usually negative, they can rarely be positive as well^[4]. This can occur during volcanic eruptions when volcanic ash is weathered into mafic tuffs with positive Ce-anomalies^[1]. The Pavlovka deposit in Far East Russia has large positive Ce-anomalies in its Fe-Mn oxyhydroxide ores^[4]. Because cerium is one of only two REEs that can obtain an oxidation number of +4, Ce⁴⁺ is absorbed into Mn(IV) oxides instead of other REEs and this results in a positive Ce-anomaly^[4].

References

Category:Geochemistry Category:Lanthanides

^ ^a ^b ^c ^d ^e ^f ^g ^h Thomas, J. B., Bodnar, R. J., Shimizu, N., Chesner, C. A. (2003) Melt inclusions in zircon. Reviews in Mineralogy and Geochemistry, 53 (1), 63–87.
^ ^a ^b ^c ^d ^e ^f Dai, Shifeng; Graham, Ian; Ward, Colin (2016). "A review of anomalous rare earth elements and yttrium in coal". International Journal of Coal Ecology. 159: 82–95.
^ ^a ^b ^c Zhong, Shihua; Seltmann, Reimar; Qu, Hongying; Song, Yingxin (2019-12-01). "Characterization of the zircon Ce anomaly for estimation of oxidation state of magmas: a revised Ce/Ce* method". Mineralogy and Petrology. 113 (6): 755–763. doi:10.1007/s00710-019-00682-y. ISSN 1438-1168.
^ ^a ^b ^c Laveuf, C.; Cornu, S. (2009). "A review on the potentiality of Rare Earth Elements to trace pedogenetic processes". Geoderma. 154 (1–2): 1–12. doi:10.1016/j.geoderma.2009.10.002. ISSN 0016-7061.

[:0-1] ^ ^a ^b ^c ^d ^e ^f ^g ^h Thomas, J. B., Bodnar, R. J., Shimizu, N., Chesner, C. A. (2003) Melt inclusions in zircon. Reviews in Mineralogy and Geochemistry, 53 (1), 63–87.

[:2-2] ^ ^a ^b ^c ^d ^e ^f Dai, Shifeng; Graham, Ian; Ward, Colin (2016). "A review of anomalous rare earth elements and yttrium in coal". International Journal of Coal Ecology. 159: 82–95.

[:3-3] Zhong, Shihua; Seltmann, Reimar; Qu, Hongying; Song, Yingxin (2019-12-01). "Characterization of the zircon Ce anomaly for estimation of oxidation state of magmas: a revised Ce/Ce* method". Mineralogy and Petrology. 113 (6): 755–763. doi:10.1007/s00710-019-00682-y. ISSN 1438-1168.

[:1-4] Laveuf, C.; Cornu, S. (2009). "A review on the potentiality of Rare Earth Elements to trace pedogenetic processes". Geoderma. 154 (1–2): 1–12. doi:10.1016/j.geoderma.2009.10.002. ISSN 0016-7061.

[1]

[2]

[3]

[4]