Original paper

Exceptionally K-rich clinoptilolite — heulandite group zeolites from three offshore boreholes off northern Japan

Ogihara, Shigenori; Iijima, Azuma

European Journal of Mineralogy Volume 2 Number 6 (1990), p. 819 - 826

23 references

published: Dec 19, 1990
manuscript accepted: Jun 19, 1990
manuscript received: Feb 7, 1990

DOI: 10.1127/ejm/2/6/0819

BibTeX file

ArtNo. ESP147050206009, Price: 29.00 €

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Abstract

Abstract Exceptionally K-rich clinoptilolite - heulandite group zeolites, in which the K content is frequently over 90 % of the extraframework cations, occur in Quaternary - Neogene marine sediments from three offshore exploration boreholes off the Japanese Islands. The clinoptilolites and heulandites have been formed by recent burial diagenesis of acidic vitric tuffs. Acidic volcanic glass fragments of Zone I have reacted with trapped sea water to form the clinoptilolites in a narrow depth interval at the top of Zone II. The crystal size and habit of clinoptilolites are uniform and unchanged throughout Zone II. The Si/(A1+Fe) ratio of clinoptilolites does not change systematically with depth and the variation of this ratio with depth correlates with the anorthite content in volcanogenic plagioclase. If the glass composition is related to the plagioclase composition, then clinoptilolite compositions should be principally controlled by the initial glass compositions and are thus not modified during burial. Most, if not all, the K cations in these clinoptilolites were inherited from the original glass. The K-clinoptilolites of Zone II become unstable due to increasing temperatures and are transformed to K-heulandites in Zone III. The difference in crystal size and habit between Zones II and III may be due to the fact that the transformation is not a cation exchange reaction but a microdissolution - precipitation process

Keywords

clinoptiloliteheulanditeburial diagenesiszeolitic zoningSi/(A1+Fe) ratio