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Geode






Geodes (Greek γεώδης - ge-ōdēs, "earthlike") are commonly independent spherical masses of resistant mineral matter that are usually hollow. The extreme filling of a geode so that it is "solid" is also common. Some people refer to completely in-filled geodes as nodules, but the two names are not always consistently used. Geodes differ from "nodules" in that a nodule is a solid mass of mineral matter, but some nodules may have a tiny void space in their interiors and the distinction between a geode and a nodule may be barely discernible if the cavity is miniscule. Geodes differ from vugs in that geodes can be separated free from any matrix, because the walls of geodes are strong enough to maintain the integrity of their initial shapes. Geodes differ from vugs in possessing an outer mineral layer which is more resistant to weathering than the host rock. As such, complete geodes commonly weather out of rock exposures and accumulate in canyons, talus, rock detritus, etc. Many geode localities occur is desert areas and are elluvial, not alluvial, meaning the geodes have not been transported by water.

The most common geodes are dominantly quartz, but geodes may be composed of other minerals such as calcite, goethite, etc. Many quartz geodes consist of concentric layers of several varieties of quartz, such as chalcedony, agate, common opal, and visibly crystalline quartz. The order of the kinds of mineral layers varies with the particular history of the formation of geodes. The interior of geodes may also contain a wide variety of independently crystallized minerals: calcite, pyrite, kaolinite, sphalerite, millerite, baryte, dolomite, limonite, smithsonite and quartz. Geodes have been found in regions that have basaltic lavas and limestones. Occasionally, geodes may be able to be mined, as in Brazil and Uruguay, when the enclosing rock is easily separable from the geode structure.

Geodes are often named according to a particular feature or mineral they exhibit or mention where the particular geodes were found. Common informal names for geodes include: quartz geodes, amethyst geodes, agate geodes, enhydro geodes, Oco geodes, Keokuk geodes, cocoanut geodes, etc. Thunder eggs may occur as geodes or nodules. See also Thunder Egg.


Note that the Spanish language cognate "geoda" simply means any crystal-lined vug, so the English meaning used here is narrower.


Classification of Geode

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Other Names for Geode

Varieties:
Enhydros

Other Information

Fluorescence in UV light:Some geodes fluoresce in UV
Health Warning:No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

Mindat.org articles about Geode

Article entries:
GeodesDave Crosby
ThundereggsDave Crosby
Rockhounding for Geodes in Remote, Rural Southern IndianaCharles Snider

Internet Links for Geode

Search Engines:
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  • Geode specimens for sale - minfind.com
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  • Specimens:The following Geode specimens are currently listed for sale on minfind.com.

    Localities for Geode

    The map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.
    (TL) indicates type locality. ? indicates mineral may be doubtful at this locality. All other localities listed without reference should be considered as uncertain and unproven until references can be found.
    Argentina
     
    • Chubut
      • Mártires Department
        • Las Plumas
    Van King
    Raúl Jorge Tauber Larry
      • Wanda mines
    Raúl Jorge Tauber Larry
    Raúl Jorge Tauber Larry; Hugo A. Peña (1970): Minerales y rocas de aplicación de la Provincia de Tucumán. Secretaría de Estado de Comercio, Industria y Minería. Dirección Provincial de Minas. Tucumán. República Argentina.
      • Capital Department
    Hugo A. Peña (1970): Minerales y rocas de aplicación de la Provincia de Tucumán. Secretaría de Estado de Comercio, Industria y Minería. Dirección Provincial de Minas. Tucumán. República Argentina.
      • Tafí del Valle Department
        • Estancia Anchilla
    R. J. Tauber Larry (2012). Visita a los cuerpos pegmatíticos de Estancia Anchilla, Departamento Tafí del Valle, Provincia de Tucum´´an.; R. J.Tauber Larry (2012). Visita a los cuerpos pegmatíticos de Estancia Anchilla, Departamento Tafí del Valle, Provincia de Tucumán.
    Raúl J. Tauber Larry (2012).
    Hugo A. Peña (1970): Minerales y rocas de aplicación de la Provincia de Tucumán. Secretaría de Estado de Comercio, Industria y Minería. Dirección Provincial de Minas. Tucumán. República Argentina.
      • Trancas Department
    Ávila, J.C. y Fogliata, A.S., 1992. Descripción de las geodas de Vipos, provincia deTucumán. Nota Breve. 1ra Reunión de Mineralogía y Metalogenia y 1ra Jornada de Mineralogía, Petrografía y Metalogénesis de Rocas Ultrabásicas. Instituto de Recursos Minerales, UNLP. Publicación 2: 29-34.
    Raúl J. Tauber Larry´s collection (2014)
    Raúl Jorge Tauber Larry
    Brazil
     
    • Rio Grande do Sul
      • Alto Uruguai region
    Jeff Scovil
    Hungary
     
    • Veszprém Co.
      • Balaton Uplands
    Kiss, G. & Molnár, F. (2006) Mineralogy And Origin Of Geodes In The Balatonfelvidék Sandstone Formation At Csopak Village, Balaton Highland, Hungary. Acta Mineralogica-Petrographica, Abstract Series 5, Szeged, p54
    India
     
    • Maharashtra
    Philip.Michelin
    Malawi
     
    • Chiwawy-Nsanje District
    Jewel Tunnel Imports
    Mexico
     
    • Chihuahua
      • Mun. de Aldama
    Karl Volkman
      • Mun. de Chihuahua
        • Barranca de Cobre (Copper Canyon)
    Gem Center USA
    USA
     
    • Colorado
      • Fremont Co.
    Minerals of Colorado (1997) E.B. Eckels
    Minerals of Colorado (1997) E.B. Eckels
      • Larimer Co.
        • Rocky Mountain National Park
    Minerals of Colorado (1997) E.B. Eckels
      • Las Animas Co.
    Minerals of Colorado (1997) E.B. Eckels
      • Rio Grande Co.
    Minerals of Colorado (1997) E.B. Eckels
      • San Miguel Co.
        • San Juan Mts
    Minerals of Colorado (1997) E.B. Eckels
    • Illinois
    Van King
    • Indiana
      • Brown Co.
        • Trevlac
    Van King
      • Lawrence Co.
        • Mitchell
    Rob Lavinsky
        • Pleasant Run Township
    Charles Snider
      • Monroe Co.
        • Bloomington
    Peter Cristofono
    • Nevada
      • Humboldt Co.
        • Lone Pine District
    USGS Bull 1538D
    • New Mexico
      • Luna Co.
        • Carrizalillo District
    NMBGMR Open-file Report OF-459
        • Cooks Peak District (Cooke's Peak District)
    NMBGMR Open-file Report OF-459
    • Tennessee
      • Sevier Co.
    Economic Geology; 1 August 1971; v. 66; no. 5; p. 777-791
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    Copyright © Jolyon Ralph and Ida Chau 1993-2014. Site Map. Locality, mineral & photograph data are the copyright of the individuals who submitted them. Site hosted & developed by Jolyon Ralph. Mindat.org is an online information resource dedicated to providing free mineralogical information to all. Mindat relies on the contributions of thousands of members and supporters. Mindat does not offer minerals for sale. If you would like to add information to improve the quality of our database, then click here to register.
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