Micas and chlorites are often weathered to vermiculite and smectite minerals under surface and near-surface earth conditions. It has been seen by a number of observations that there is a certain weathering sequence of micas and chlorites toward smectite minerals which are ultimately hydrated 2:1 expandible layer silicate. This prompted us to undertake experimental alteration studies of micas and chlorites in order to gain a better understanding of factors controlling weathering processes.
Potassium was extracted from the 1-2μm fraction of 2 M1 muscovite by BaCl₂ and from the 0.2-2μm fraction of 1 M phlogopite by CaCl₂ to replace with hydrated interlayer cations. The release of K was initiated at certain preferential layers (perhaps structurally weak spots) and then followed from layers next to those where K had previsouly been released, so that there was a strong tendency to form a zonal structure. The experiments with coarser fractions of the phlogopite, however, showed a tendency to form a rather homogeneous mixed-layer structure at intermediate stage of hydration. Re-entry of K in the vermiculitized micas resulted in the return of original mica structures, 1M, 2M, 3T etc., suggesting that structural heredity exists.
Experimental alteration of chlorite to vermiculite required certain structural disruption in the interlayer hydroxide sheet of chlorite prior to its selective disso-lution. This can be achieved by dehydroxylation of the hydroxide sheet, or by oxidation in the case of Fe²⁺-bearing chlorites. A clinochlore sample was altered to vermiculite by treating a dehydroxylated sample with a weak acid in the presence of Na⁺. With the oxidation technique using saturated Br solution, a chamosite sample was converted into vermiculite whereas an Fe-clinochlore sample was altered into a high charge corrensite (1: 1 regular mixed layer of vermiculite and chlorite).
These experimental results were discussed in the light of observations on mineral weathering in nature and important problems desired to be solved in near future were presented.

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Mode of occurrence and mineralogy of clay minerals in Komaki halloysite deposit, Shimane Prefecture, southwest Japan, and its surrounding granitic rocks have been investigated by means of X-ay powder diffraction and transmission and scanning electron microscopes.
The Komaki deposit is composed of two are bodies which are sharply bordered from the host rocks. The clay minerals of ores are composed of halloysite, kaolinite and mica clay mineral associated with a small amount of smectite. The rocks in the deposit are divided into three alteration zones based on the clay mineral assemblages: zone I (halloysite zone), zone II (kaolinite and halloysite zone), and zone III (kaolinite and mica clay mineral zone). The halloysite zone appears at the center of deposit, while the kaolinite and mica clay mineral zone occurs in the margin through the halloysite and kaolinite zone. Clay-veins (ca.0.1-5 cm in width) which are filled with halloysite, kaolinite, mica clay mineral and smectite are observed in the deposit. They have mainly N 0-10°W, E-W and N 30°-60°W of strike and nearly vertical dip.
In the surrounding granitic rocks, the altered minerals and the clay-veins situated at higher levels are mainly composed of halloysite and kaolinite, whereas mica clay mineral and smectite are mainly found at lower levels. The clay-veins have mainly N0°-10°W, E-W and N30°-60°W of strike and nearly vertical dip. The fractures found in the studied area seem to be formed by a regional lateral compression of NW-SE direction
Most of the clay deposit was formed by hydrothermal alteration of fractured felsitic rocks. The constituent minerals of clay-veins and major altered minerals in the surrounding rocks may be formed by a hydrothermal activity rather then weathering.

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Natural zeolites form under a wide range of environments from cold deep-sea oceanic bottom sediments to hot hydrothermal alteration and from the Earth's surface to a great burial depth. Based on the states of water related to zeolite formation, the occurrence of zeolites is classified into several types: in order of increasing temperature, 1) deep-sea oceanic bottom. 2) weathering in arid to semi-arid regions, 3) saline, alkaline lakes, 4) percolation of meteoric water, 5) burial diagenesis. 6) hydrothermal alteration and contact metamorphism, and, 7) primary magmatic. Volcanic glass in ashes and vitric tuffs is by far most suitable for raw material of natural zeolites. Specific zeolite reaction series in different types of occurrence cause characteristic zonal distribution of unaltered glass zone, zeolite zone, and authigenic feldspar zone when appeared. In saline, alkaline lake deposits, for example, the horizontal zonal distribution is attributed to chemical gradient in pore water. In thick marine sequences, on the other hand, the vertical zonal distribution is attributed primarily to geothermal gradient.
Rate of zeolitic reactions is a big geological problem to be solved, though it is difficult. The difficulty results largely in recognizing real reacting time in nature. The reacting time is able to be estimated either from the age of the youngest zeolitized tuff in alkali soil profiles and in saline, alkaline lake deposits, or from very slow rate of sedimentation of phillipsite-containing pelagic sediments. The rate of the analcime to albite transformation during burial diagenesis is estimated to be approximately 400, 000 years this figure is known from the thickness of a transitional zone (analcime coexisting with albite) between Zone III (analcime) and Zone IV (albite) using the burial history diagram as shown in Fig.4.
Zeolites in any types of occurrence change ultimately to thermodynamically stable alkali feldspars or other non-zeolite minerals through intermediate zeolites, such as analcime and laumontite, due to the increase of temperature and pressure, to the increase of concentration of pore water, or to ageing. As a result, zeolite assemblage tends to be simpler in the later stage than in the early stage (Fig.5). This probably reflects on the fact that the number of zeolite species, except for veins and vugs, decreases markedly with ascending geologic age of host rocks (Fig.6).

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Analcime and wairakite are common species of zeolitites as alteration product. However, the phase relation, especially the crystal chemical relationship between the two minerals has not been clarified.
Synthetic investigation on the phase relations in the analcime solid solution-wairakite system including long-run experiments for 50 days shows that the anal-cime group is composed of analcime I (cubic analcime), analcime II (non-cubic analcime), wairakite I (disordered wairakite) and wairakite II (ordered and strictly monoclinic wairakite). The analcimes have always sharp (400) reflection and the relative intensity I₄₀₀/I₂₁₁ is 1.6±0.4. Morphology of the analcime I changes usually from a hexahedral form to an icositetrahedral form during crystallization, but the analcime II exhibits nearly always a (100) + (211) form. The relative intensity I₄₀₀/I₂₁₁ of the wairakite II (1.0±0.4) is fairly small compared with that of the wairakite I (1.4±0.5). Although morphology of the wairakites is not so simple, most of the wairakite I show a (111) + (100) form and most of the wairakite II a (111) + (211) + (100) + (110) form.
The isobaric diagrams of the analcime solid solution-wairakite system obtained at PH₂O=1, 000 bars and reaction time=50 days suggest that a continuous isomorphous series does not exist between analcime and wairakite and that many of the minerals having intermediate chemical compositions between analcime and wairakite can be regarded as calcian analcime (analcime II)

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Decoration-method, which was newly developed as original technique, was applied to the examination of surface microtopographies for diagenetic clinoptilolite.
Natural materials were treated in a weak alkaline solution of Na₂CO₃ at a range from 150 to 200°C. Fine particles of silica in the solution deposit along the steps on the crystal faces and decorate the original growth steps. The particles develop largely by a gold evaporation operation in vacuum and can be observed the crystal growth spirals by scanning electron microscope.
Clinoptilolite specimens were obtained from Miocene dacitic tuff at two localities, Oga and Futatsui, Japan. All the crystals observed show spiral patterns on the (010) face, though other faces exhibit no growth pattern. The crystal distinctly are decorated along the spiral steps, and the height of steps is assumed to be that of unit-cell size.
The patterns of Oga specimens are rectangle correlating to a orthorhombic symmetry. Some spiral patterns have square pits which are attributable to the dislocation site on the center. The patterns of Futatsui specimens have no etch pits, and vary from polygonal to circular. Many growth centers are observed on the (010) face, and the patterns are more complicated as compared with that of Oga specimens. Generally, polygonal spirals are expected under low temperature and low supersaturation conditions than for circular spirals, and also narrower step separations are expected for crystals grown from higher supersaturation. Geological evidence shows that the present zeolite crystals were formed under hydrothermal condition. It is suggested that Futatsui clinoptilolite crystals were produced under higher temperature and higher supersaturation condition than Oga specimens.

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In some zeolites, the symmetry which was determined by optics is lower than that determined by X-ray diffraction. The crystal symmetry is attributed to various atomic ordering which is produced during growth. When vicinal faces on the crystal face are symmetrically inclined to the mirror plane, ordered structures are symmetrical with respect to the mirror plane, resulting in twinning. On the vicinal face normal to the mirror plane, the corresponding structure becomes statistically disordered and the mirror plane is maintained during growth.

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