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The alteration of leucite-bearing rocks; a possible mechanism

Ciriaco Giampaolo, Raimondo F. Godano, Bruno Di Sabatino and Eugenio Barrese
The alteration of leucite-bearing rocks; a possible mechanism
European Journal of Mineralogy (December 1997) 9 (6): 1277-1291


A series of rocks collected from a single lava flow near Lake Bracciano (Rome) shows progressive stages of analcimization. This paper presents a chemical study of these rocks with calculations of gains and losses from the bulk-rock chemical composition based on atomic percent. With increasing alteration, Na increase is counterbalanced by a decrease in K, Ca and Mg; total iron content is constant but ferrous Fe increases. Mineral phases, either as phenocrysts and/or as laths present in the volcanic groundmass, have been analyzed by EMPA. In addition to leucite altered to analcime, feldspars and pyroxenes converge towards close composition with progressive analcimization. Plagioclases reach labradorite-bytownite compositions and a ternary Na-Ca-K member develops. Chemical variations observed either in bulk-rock composition or among minerals suggest that the analcimization process occurs in an open, reducing environment and that a partial rearrangement of alkalis occurs within the rock. Analcimization also appears to be linked to the rapid cooling of the rock and to the formation of zeolites which are subsequently transformed into analcime.

ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 9
Serial Issue: 6
Title: The alteration of leucite-bearing rocks; a possible mechanism
Affiliation: Universita di Roma Tre, Dipartimento di Scienze Geologiche, Rome, Italy
Pages: 1277-1291
Published: 199712
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 26
Accession Number: 1999-013177
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Secondary Affiliation: Universita di Chieti "G. D'Annunzio", ITA, ItalyUniversita della Calabria, ITA, Italy
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 199905
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