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A low temperature experimental alteration of a rhyolitic obsidian

Saverio Fiore, F. Javier Huertas, Kazue Tazaki, Francisco Huertas and Jose Linares
A low temperature experimental alteration of a rhyolitic obsidian
European Journal of Mineralogy (June 1999) 11 (3): 455-469


The most evident chemical change found in the experimental alteration of nine samples of obsidian by distilled water in an open system (T 85 + or - 5 degrees C, pH 5.5-6) for < or = 1717 h is the loss of alkalis and the gain of H (sub 2) O. Statistical analysis showed that inwards diffusion of molecular water into the bulk glass takes place during the early stages of alteration, followed by cation (super +) -H (sub 3) O (super +) or cation (super +) -H (super +) interdiffusion and changes within the glass structure as well as disruption of the silica network at the glass-solution interface. The structural reorganization of the glass is accompanied by the formation of flake-leaf-needle morphologies, perhaps representing three steps of local crystallization within the glass, the acicular material probably being halloysite. The specific weight-loss leach rate of the rhyolitic obsidian is very slow, at 1.5 + or - 0.51 X 10 (super -8) g/m (super 2) /s. Leach rates in order of mobility are Na > Si = K > Ca > Ti = Al for major elements, and Pb > Lu > Er > Zn > La > Rb > Ce for trace elements.

ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 11
Serial Issue: 3
Title: A low temperature experimental alteration of a rhyolitic obsidian
Affiliation: CNR, Istituto di Ricerca sulle Argille, Tito Scalo, Italy
Pages: 455-469
Published: 199906
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 41
Accession Number: 1999-046895
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
Secondary Affiliation: CSIC, ESP, SpainKanazawa University, JPN, Japan
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United KingdomTwickenhamUKUnited Kingdom
Update Code: 199916
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