The surface areas of bulk chrysotile asbestos and mechanically opened fibers were measured for samples with different degrees of softness. The results were evaluated in order to find interrelationships between softness, defibrillation character and morphology of chrysotile.
It was revealed that the softness of chrysotile asbestos has correlation to the surface area of bulk chrysotile which is effected mainly by the cementing area between close packed fibrils and by the amount of interfibrillar material. The softness also relate directly to the defibrillation character which was shown by the relationship between the degree of surface area increase and treating time.
From these discussion, it was concluded that the softness of chrysotile asbestos indicate the easiness of defibrillation when a external force is applied to the fiber bundle, and the easiness of defibrillation is dependent on the bonding strength of individual fiber, which is effected mainly by the existence of interfibrillar material.

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Phase transformations of sepiolite under hydrothermal conditions were investigated by treatment of two varieties of sepiolite (α-and β-type) in the temperature range from 150°to 700°C at water vapor pressures of 250, 500 and 1000kg/cm², respectively.
The products were examined by means of X-ray diffraction technique, thermal analysis and infra-red absorption spectroscopy.
The results obtained are as follows:
Under water vapor pressures of 500kg/cm², a-sepiolite is stable below 330°C. Above this temperature, it transforms into “hydrated talc”(330°-460°C) and talc (>460°C).β-seniolite changes into “hvdrated talc”(310°-530°C) andtalc (>530°C).
Therefore, it was found that an intermediate phase such as “hydrated talc” comes between sepiolite and talc in their stability fields. It seems that the revealed difference of the two sepiolites depends on the difference of their crystallinity and their length of fibers.

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Kuchinoerabujima is a small volcanic island which is situated at Tokara Islands, southern part of Kyushu, Japan. And the climate of the island, one of the factors affecting weathering, is warm and very wet.
In the island, alteration phenomena of the sedimentary volcanic ashes which belong to augite-hyperthene andesite were observed. And the sequence of changes of the sediments from upper to lower layer was studied mineralogically and chemically, and following results were obtained.
1) At surface layer, amorphous silico-alumina and hydrous sesquioxides as secondary minerals are detected. The amount of those clay-size materials is very little in quantity.
2) In the second layer, the decomposition of plagioclase obviously proceeds and allophane, halloysite and gibbsite are formed. The grain size of those minerals is generally very small except gibbsite, which cementizes the particles of volcanic ashes and grows about 10-20μin size.
3) In the third layer which developes at the part of 2-3 m from the surface (vertical width 0.5-2 m), halloysite, illite, 14Å-mineral and iron hydroxide are found. This layer is very clayey and is dark-brownish in color and also it represents an illuvial zone. The amounts of Si0₂, Fe₂0₃, K₂0 and Mg0 of the clay separated from this layer are relatively rich compared with the components of the clays obtained from other layers.
4) Under the third layer, allophane and gibbsite are mainly formed when the layer is composed of coarse particles. And as the layer becomes more clayey, halloysite content is more rich. The molar ratio, Si0₂/Al₂0₃, of the clay is about 2.

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