Crystallization of radiolaria amorphous silica in diagenesis

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This work has been done to elucidate diagenesis based on mineralogy and crystallography. Shell of microfossil radiolaria consists of amorphous silica and is known to crystallize in alpha quartz in diagenesis. A degree of crystallization is considered to have a close relation with diagenesis and can be estimated by crystallinity of alpha quartz of the shell. Crystallinity of the shell of radiolaria canbe determined by measuring the line width of X-ray powder pattern.Specimens of radiolaria were obtained from mudstone, slate and chert of Jurassic period in Shikoku Sanbagawa belt. Amorphous silica of radiolaria in deep sea was used as standard. Every X-ray diffraction pattern of radiolaria shows unoriented powder pattern of alpha quartz. No diffraction pattern was observed from radiolaria in deep sea indicating amorphous silica. The line width becomes sharper in order of madstone, chert and slate. The results agree with the degree of diagenesis.The degree of diagenesis was also estimated from particle size of alpha quartz of radiolaria shell. Specimens of radiolaria were obtained from sedimentary rocks in Eastern part of Shikoku. Particle size was observed under Scanning Electron Microscope. The particle sizes are distributed in the range between 2 and 15 micron depending on diagenesis.Heat treatment of amorphous silica of radiolaria shell was carried out. Amorphous silica crystallized in alpha quartz at 600 and 700 ﾟC for 1 day.In conclusion crystallinity and particle size of alpha quartz of radiolaria shell have close relations with the degree of diagenesis.