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Periodic Table--Lithium

Lithium has two naturally-occurring stable isotopes, 6Li (7.5 %) and 7Li (92.5 %). Lithium isotopes fractionate substantially during a wide variety of natural processes, including mineral formation (chemical precipitation), metabolism, ion exchange (Li substitutes for Mg and Fe in octahedral sites in clay minerals, where 6Li is preferential over 7Li), hyperfiltration, and rock alteration (Morozova and Alferovskiy, 1974; Chan and Edmond, 1988; Fritz and Whitworth, 1994). Therefore, isotopic compositions of Li can provide a basis for distinguishing various lithologic sources of cations in catchment waters and/or to trace water affected by the processes.

In the past, the ease with which Li fractionates has made laboratory isotopic analysis very difficult. Fortunately, recently developed techniques have been used to examine the Li isotopic compositions from thermal waters of Yellowstone National Park (Bullen and Kharaka, 1992). Because the isotopes will fractionate during hydrothermal processes, significant variations observed in the 7Li/6Li ratios distinguished water derived from marine sedimentary rocks and water derived from hydrothermally altered igneous rocks, thereby providing valuable information regarding regional ground-water flow paths.

In addition, lithium isotopes have recently become a source of quality control on manufactured lithium reagents (Qi et al., 1997). Several reagents were found to be artificially depleted in 6Li significantly compared to terrestrial materials, indicating that many lithium reagents used in chemical experiments are in fact 6Li-depleted and do not accurately reflect the atomic and/or molecular weights of these reagents. Large quantities of 6Li were removed from Li reagents for use in nuclear weapons. The remaining Li was then sold to chemical companies and found its way into reagents on chemists' shelves. Sometimes this Li makes its way into streams and it can be easily identified.

Source of text: This review was assembled by Eric Caldwell, primarily from Nimz (1998).

Bullen, T.D. and Kharaka, Y.K. (1992). "Isotopic composition of Sr, Nd, and Li in thermal waters from the Norris-Mammoth corridor, Yellowstone National Park and surrounding region." In: Water-Rock Interaction. Proceedings of the 7th International Symposium on Water-Rock Interaction, Balkema Publishers, Rotterdam, p. 897.
Chan, L-H. (1987). "Lithium isotope analysis by thermal ionization mass spectrometry of lithium tetraborate." Anal. Chem., 59: 2662.
Chan, L-H. and Edmond, J.M. (1988). "Variations in lithium isotope composition in the marine environment: A preliminary report." Geochim. et Cosmochim. Acta, 52: 1711.
Fritz, S.J. and Whitworth, T.M. (1994). "Hyperfiltration-induced fractionation of lithium isotopes: Ramifications relating to representativeness of aquifer sampling." Water Resour. Res., 30: 225.
Morozova, I.M. and Alferovskiy, A.A. (1974). "Fractionation of lithium and potassium isotopes in geological processes." Geochem. Int., 11: 17.
Nimz, G.J. (1998). "Lithogenic and Cosmogenic Tracers in Catchment Hydrology." In: C. Kendall and J.J. McDonnell (Eds.), Isotope Tracers in Catchment Hydrology. Elsevier, pp. 247-290.
Qi, H.P., Coplen, T.B., Wang, Q.Zh. and Yang, Y.H. (1997). "Unnatural Isotopic Composition of Lithium Reagents." Anal. Chem., 69, 19: 4076-4078.
Xiao, Y.K. and Beary, E.S. (1989). "High-precision isotopic measurement of lithium by thermal ionization mass spectrometry." Int. J. Mass Spec. Ion Proc., 94: 101.
Related Links
Periodic Table
Fundamentals of Stable Isotope Geochemistry
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Isotope Publications
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