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Document Type

Research

Abstract

White, compacted masses of kaolinite are common in the famous geodes from the upper mudstone unit of the lower Warsaw Formation around Keokuk, Iowa. X-ray diffraction studies of the fine silt-size, pseudhexagonal grains show the kaolinite to be exceptionally well crystallized and free from impurities. Stacking faults are produced by grinding the kaolinite, which have a marked effect on X-ray patterns. The relationship of kaolinite to other mineral euhedra in geode cavities indicates that kaolinite formed early in geode history. Several lines of evidence suggest that the kaolinite originated from the fine-grained silicate residue remaining after acid dissolution of early diagenetic calcareous concretions, the progenitors of geodes. The kaolinite formed in an acid environment into which aluminum was introduced to react with the layer silicate "wreckage" from the concretions.

Publication Date

1963

Journal Title

Proceedings of the Iowa Academy of Science

Volume

70

Issue

1

First Page

261

Last Page

279

Copyright

© Copyright 1963 by the Iowa Academy of Science, Inc.

Language

EN

File Format

application/pdf

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