Crystallization of radiolaria amorphous silica in diagenesis

放射虫无定形二氧化硅在成岩作用中的结晶

• 批准号: 08454159
• 负责人: KOTO Kichiro
• 金额: $ 3.9万
• 依托单位: The University of Tokushima
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 1996
• 资助国家: 日本
• 起止时间: 1996 至 1998
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08454159/
• 关键词: radiolaria; earth crust; alpha quartz; amorphous silica; microfossil; X-ray powder pattern; Sanbagawa; Jurassic period; X線回折プロファイル

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.

这项工作是为了阐明基于矿物学和晶体学的成岩作用。微化石放射虫的外壳由无定形二氧化硅组成，在成岩作用中结晶于α石英。结晶程度被认为与成岩作用密切相关，可以通过壳中α石英的结晶度来估计。放射虫壳的结晶度可以通过测量x射线粉末谱线宽来确定。在四国三川带侏罗纪泥岩、板岩和燧石中采集了放射虫标本。以深海放射虫的无定形二氧化硅为标准。放射虫的x射线衍射图均为α -石英的无取向粉末状。深海放射虫未见衍射图，表明其为无定形二氧化硅。线条宽度按泥岩、燧石和板岩的顺序逐渐变细。结果与成岩作用程度一致。根据放射虫壳α -石英的粒度，对其成岩作用程度进行了估计。从四国东部的沉积岩中获得了放射虫标本。扫描电镜下观察颗粒大小。根据成岩作用的不同，颗粒大小分布在2 ~ 15微米之间。对放射性虫壳的无定形二氧化硅进行了热处理。无定形二氧化硅在600和700的温度下结晶1天。综上所述，放射虫壳α石英的结晶度和粒度与成岩作用程度密切相关。