Occurrence of Analcime of Karaj Formation in Semnan Province, Central Alborz, Iran

The occurrence of analcime in the Karaj Formation, Eocene, at Kuh-e-Astaneh, Abdolabad and Kuh-e-Cheheltan in Semnan province is discussed based on the field and thin section studies, XRD, SEM and chemical analyses of host rocks. Analcime is the only zeolite occured in the Kuh-e-Astaneh and Abdolabad regions, while at Kuh-e-Cheheltan both analcime and clinoptilolite occur in tuffs of the latter region. In all these regions analcime is associated with abundant quartz, lesser amounts of feldspar, opal-CT, smectite, dolomite, calcite and mixed-layered smectite. The host rocks of analcime in the regions are rhyolitic, rhyodacitic and dacitic tuffs. Occurrences of the associated minerals and the absence pumpellyite and other characteristic metamorphic minerals are in favor of a diagenetic, rather than metamorphic, formation of the zeolites in the study regions.