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3. Fisher, I. S. 1977. Distribution of Mississippian geodes and geodal minerals in Kentucky. Economic Geology 72 (5): 864-69.
4. Folk, R. L., and J. S. Pittman. 1971. Length-slow chalcedony: A new testament for vanished evaporates. Journal of Sedimentary Petrology 41:1045-58.
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