Analcime in tuffs of Karaj Formation, Kuh-e-Astaneh, Western Semnan, Central Alborz, Iran

The occurance of analcime in the Karaj Formation of Kuh-e-Astaneh, is described based on the field study, XRD, SEM and chemical analyses of host rocks. The analcime mineral is associated with abundant quartz, lesser amounts of feldspar and a regular mixed-layered smectite. The absence of high silica zeolites, clinoptilolite or mordenite, as precursors in the samples of high K/Na ratio, are evidences indicate that the analcime formed directly from vitric tuffs of The Karaj Formation in a high saline basin prior to burial. All evidences are in favor of diagenetic character of analcime in this region.