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Published October 1977 | public
Journal Article

Mg and Ca isotopic study of individual microscopic crystals from the Allende meteorite by the direct loading technique


We have developed a direct loading technique for determining the isotopic composition of Mg in chemically unseparated samples. This technique has a sensitivity and precision comparable with those of the conventional technique of analyzing pure Mg salt and eliminates contamination introduced during the chemical separation of Mg. This results in a significant reduction in sample size required for an analysis. This technique was combined with other characterization techniques of microscopic samples (e.g. optical microscopy, SEM, EPMA), and was applied to four single crystals of pure phases from an Allende inclusion ranging in size from 25 to 150 μm. Using a total sample of 4 μg, we found an anorthite crystal showing an enrichment in ^(26)Mg of 10% and were able to construct an ^(26)Al-^(26)Mg isochron which confirms our previous results obtained on macroscopic samples of the same inclusion. The isotopic composition of Ca was also measured along with Mg, on a directly loaded anorthite crystal from this inclusion, during the same mass spectrometer run and was shown to be essentially normal. Thus, the direct loading technique is applicable to Ca and will be useful in a correlative study of isotopic effects of different elements on individual microscopic samples. The extension of this technique to other elements appears feasible but will require extensive testing to control possible interferences.

Additional Information

© 1977 Published by Elsevier Ltd. Received 15 March 1977; accepted in revised form 27 June 1977. We gratefully acknowledge Dr. Jean-Paul Revel's generosity in permitting and helping us to use the scanning electron microscope. We thank Dr A. L. Albee for ready access to the microprobe facility and Dr C. R. Lagergren of Battelle Pacific Northwest Laboratories for providing us with the design of small V-shaped filaments. Goading by Dr. F Begemann caused us to complete the description of this procedure. The calligraphy of Mr. Read Lee is appreciated. This work was supported by NSF grant PHY 76-02724 and NASA grant NGL 05-002-188.

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