Original paper

The alteration of leucite-bearing rocks: a possible mechanism

Giampaolo, Ciriaco; Godano, Raimοndο F.; Sabatino, Bruno Di; Barrese, Eugeniο

European Journal of Mineralogy Volume 9 Number 6 (1997), p. 1277 - 1292

26 references

published: Dec 2, 1997
manuscript accepted: May 12, 1997
manuscript received: Feb 13, 1996

DOI: 10.1127/ejm/9/6/1277

BibTeX file

ArtNo. ESP147050906016, Price: 29.00 €

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Abstract 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.


analcimizationalterationfeldsparspyroxenesleuciteanalcimezeolite bulk-rock chemical analyses