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).
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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.,
||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,
||Xiao, Y.K. and Beary, E.S. (1989). "High-precision isotopic measurement
of lithium by thermal ionization mass spectrometry." Int. J. Mass Spec.
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