This study focused on the upper parts of Karaj Formation in Damavand-Firuzkoh area. Field study indicated that the green tuffites of Karaj Formation in Kilan, Hesarbone, and Zarindasht irregularly altered and changed to zeolite and bentonite. Microscopic studies of zeolitic tuffites have shown that the main components of these tuffites are altered glass shards. The shards changed to zeolites from their margins. In addition to zeolite, clay minerals also changed to glass shards. Scanning Electron Microscopic studies confirmed the change of glass shard to zeolite and clay mineral from their margins. The presence of clinoptilolite and carbonate impurity in vitric altered tuffite are determined by thermal curves tests
(TG & DTG). Also, X-ray showed clinoptilolite, crystobalite as major mineral and muscovite, montmorillonite as minor mineral in these tuffites. On the base of XRF and ICP, chemical composition of these tuffites are in the range of acid to intermediate rocks compositions. Chemical composition of altered and unaltered tuffites is unique. Base on the petrological studies, the componential magma of the tuffites is calc alkaline. Spider diagrams indicated the enrichment of K, Ba, Th, Rb, which is characteristic of arc magmatism.

The bentonites of Aftar region, with average of 15 meters thickness and about 10 km long, are volcanoclastic sequence of Semnan Formation that formed in a shallow sea water environment. Based on the field, XRD data, microscopic and scanning electron microscopic (SEM) studies, as well as chemistry, the bentonite beds contain zeolites (clinoptilolite and mordenite), gypsum, calcite, celestine, opal, quartz, crystobalite and aragonite associated with clay minerals. XRD data of air-dried, glycolated and heated of clay fractions show the majority of the clay minerals are of swelling and of dioctahedral, smectite types. FTIR spectra, in agreement with chemical analyses data, reveal that the smectites are of Wyoming type (SWy-2) montmorillonite. The structural formula unit of representative clay of Aftar region, based on 11 oxygens, is:

(Ca_0.057Na_0.270K_0.030)(Al_1.515Mg_0.313Fe_0.109Ti_0.010)(Si_4.015O₁₀)(OH)₂.

Based on the composition of tuff and bentonites, the bentonites appear to be derived from alteration of acidic (dacitic to rhyolitic) tuffs of Eocene age in a relatively basic environment. Relatively stable smectites and zeolites are formed by dissolutim of less stable glass of vitric ash that was present in tuff during variation in basic environmental conditions.

In order to investigate the alteration products of rhyolitic tuffs under alkaline hydrothermal condition, samples of acidic pyroclastic rocks from Darabad area (N-E Tehran) were selected. Rock samples were examined under petrographic microscope, X-Ray powder diffraction, X-Ray Fluorescence and were eventually powdered and mixed with Na⁺ and K⁺ bearing solutions in hydrothermal autoclaves. The effect of changes in temperature, time and concentration of cations in solution, alteration of aforementioned tuffs have been studied. The solutions with 1.25- 7.5 mol/lit cation concentrations from KOH and NaCl salt have been prepared and used in hydrothermal experiments in 100 °C and 150 °C. The results revealed that in alteration of rhyolitic tuffs, in presence of KOH and NaCl solutions, with increasing temperature, concentration of Na⁺ and pH, the quality of quartz decreases and the quality of albite increases (sodic alteration). At 150 °C  and high concentration of Na⁺ and K⁺ (7.5 mol/lit), quartz dissolves completly, albite changes to orthoclase with cationic exchange of Na⁺ by K⁺ (potassic alteration) and forms hydroxy sodalite (zeolitic alteration). XRD studies proposed cubic system with unit cell dimensions of a₀= b₀= c₀= 8.8760 Å for hydroxy sodalite.

The study area (Kalateh-No) is located in NW of Gonabad city in Khorasan Razavi Province. This area is located in geotectonic Lut Block zone. The rock types are mainly of volcanic and subvolcanics. The most important alteration zones are silisification, propylitic, argillic, serisitic and quartz-serisit-pyrite. The mineralizations have formed by intrusion of hydrothermal fluids of monzodiorite porphyry and alteration of rocks along its path. The mineralogical compositions are quartz, illite, muscovite, montmorillonite, albite, orthoclase, gypsum and iron phases (pyrite and hematite). The chemical composition shows the high percentage of SiO₂ (average: 66/97%) and the amount of Alumina (Al₂O₃) is low (average: 17/67%). The meteoric water and hydrothermal fluids caused two types of supergene and hydrothermal clays, which supergene clays are deposited at the top clays hydrothermal clays.