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Geodes

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Encyclopedia of Sediments and Sedimentary Rocks

Part of the book series: Encyclopedia of Earth Sciences Series ((EESS))

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Introduction

Geodes are nodules (i.e., mineral aggregates having a composition that contrasts strongly with that of the surrounding rock) containing an interior cavity lined with macroscopic crystals (i.e., crystals sufficiently large to be distinguishable without magnification). Geodes occur primarily within limestones, dolomites, and mudrocks, but some are found in volcanic rocks. The term geode is largely synonymous with “vug” (a crystal-lined cavity), but has the additional connotation that the object has, or could, weather free by virtue of its compositional and textural distinctiveness from the host rock. The sizes and shapes of geodes vary widely, but most are in the range of 5 to 10 cm across and roughly spherical or oblate. Geodes are recognized as a group partly on the basis of their appearance and distinctiveness, in particular their attractiveness to mineral collectors. (Figure G2).

Figure G2
figure 2

(A) Geode from a volcanic host rock. A chalcedony rim followed by coarse quartz...

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Author information

Authors and Affiliations

  1. Department of Geological Sciences, University of Texas, Austin, TX, 78712, USA

    Kitty L. Milliken

Authors
  1. Kitty L. Milliken
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Editor information

Editors and Affiliations

  1. School of Geography and Geology, McMaster University, 1280 Main St West, Hamilton, ON, L8S 4K1, Canada

    Gerard V. Middleton

  2. Department of Geography, University of British Columbia, Vancouver, BC, V6T IZ2, Canada

    Michael J. Church

  3. Department of Earth Sciences, University of Waterloo, Waterloo, ON, N2L 3G I, Canada

    Mario Coniglio

  4. Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, 21218, USA

    Lawrence A. Hardie

  5. Department of Earth Sciences, University of Western Ontario, London, ON, N6A 5B7, Canada

    Frederick J. Longstaffe

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© 1978 Dowden, Hutchinson & Ross, Inc.

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Milliken, K.L. (1978). Geodes. In: Middleton, G.V., Church, M.J., Coniglio, M., Hardie, L.A., Longstaffe, F.J. (eds) Encyclopedia of Sediments and Sedimentary Rocks. Encyclopedia of Earth Sciences Series. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-3609-5_96

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  • DOI: https://doi.org/10.1007/978-1-4020-3609-5_96

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  • Publisher Name: Springer, Dordrecht

  • Print ISBN: 978-1-4020-0872-6

  • Online ISBN: 978-1-4020-3609-5

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