Dear Dr. Emmermann,

Here is a reference for carbon isotopic fractionation from experimental
precipitation of aragonite and calcite:

        Romanek, C.S., Grossman, E.L., and Morse, J.W. (1992)  Carbon
isotope fractionation in synthetic aragonite and calcite:  Effects of
temperature and preciptiation rate.  Geochim. Cosmochim. Acta, V. 56:1,
p419-430.

Eileen

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