Research Training ProgramSmithsonian
Institution
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 Tara S. Kirkpatrick Mount Holyoke College South Hadley, Massachusetts |
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| Michael Wise, Ph.D. Supervising Scientist Department of Mineral Science |
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| "To be given the opportunity of
continuing my research with Dr. Wise and producing a publication has
been the highlight of my undergraduate career. " |
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ABSTRACT |
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There has been debate among scientists for years over whether fine-grained lepidolite bodies within zoned, rare-element granitic pegmatites crystallize directly from the original melt (primary origin), or during an altogether unrelated event (secondary origin). This debate is undoubtedly important because lepidolite, a lithium-rich mica, is a common constituent within pegmatites and is often found in association with gem pockets. These pockets are economically important for their abundance of large tourmalines, beryls and other minerals. Therefore, knowing the petrogenesis of the lepidolite could lead to a better understanding of the formation of these pegmatite pockets and pegmatites overall. As a result, developing a criteria for distinguishing between primary and secondary lepidolite has been key. In this study, an attempt was made to accomplish this by analyzing many different lepidolite samples' major and trace element chemistry and thin-sections for textural information. Last summer's research took a broad approach to the problem and involved looking at lepidolite assemblages from a number of localities across North America. However, this summer's research narrowed its scope to one specific locality, the Stewart Pegmatite in Southern California. The Stewart Pegmatite was chosen because its lepidolite bodies exhibited many different textures and mineralogies. To date, the chemistry analysis has shown that all of the samples do not carry the same geochemical signature. Whether it could be due to crystallization at different times, or crystallization from different parental magmas, still remains to be determined. As for the textural aspect of this study, criteria are being developed with further thin-section analysis. Once it is developed, though, the criteria will be applied (based on the Stewart lepidolite bodies as a model) to lepidolite bodies from other localities. There are plans for continuing this research as an undergraduate thesis with plans of submitting a publication in the spring of 1997.