The mineralogical properties of the kaolin mineral from the Zao Mine, Yamagata Prefecture are made clear from the optical properties, chemical analysis, X-ray powder pattern, thermal properties, and electron micrograph. The optical properties, chemical analysis, thermal properties and electron micrograph agree to those of halloysite. The number of the powder lines of the mineral is more than that of halloysite, although, in the part of the powder lines, diffuse character is more clearly shown than in the powder lines of typical kaolinite. From these points of view, it is concluded that the mineral corresponds to a variety of halloysite which shows higher crystallinity than the ordinary one.
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