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A new model of agate geode formation based on a combination of morphological features and silica sol-gel experiments

Charles Brian Howard and Avinoam Rabinovitch
A new model of agate geode formation based on a combination of morphological features and silica sol-gel experiments
European Journal of Mineralogy (September 2017) 30 (1): 97-106

Abstract

Agates are unable to be reproduced in a laboratory environment, and hence the mechanism of their formation remains unknown. Present hypotheses regarding genesis are thus, inevitably, speculative. We describe novel experiments, at room temperature and pressure, producing banded amorphous silica gel (via a sol-gel transition) whose morphology is compared to that of agates. In addition, macro- and microscopic examination of agates from several sites revealed some distinctive physical features: surface pitting, indentations of the agate bands, the variation in morphologies of the bands, thinning and narrowing of the bands around the indentations and the escape tubes, shapes of the coloured impurities and persistence of the sharp angle of the bands at sector boundaries. These observations and experimental data lead us to conclude that agates can be formed in four stages: sol-gel transition with concomitant band formation, formation of escape tubes, rapid crystallization from multiple nucleation sites and late dissolution/recrystallization of the inner layers.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 30
Serial Issue: 1
Title: A new model of agate geode formation based on a combination of morphological features and silica sol-gel experiments
Affiliation: Macabee Health Fund, Department of Orthopedics, Beer-Sheva, Israel
Pages: 97-106
Published: 20170905
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 30
Accession Number: 2017-085935
Categories: Mineralogy of silicatesSedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Secondary Affiliation: Ben Gurion University of the Negev, ISR, Israel
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201745
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