生体鉱物化作用によるパイライトの生成 : ケイ藻中に生成したパイライト

概要

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Biomineralizations of pyrite has been found inside of diatom cell sludge(Hedoro) of Lake Nakaumi. Direct observations by using SEM equipped with BSI, and EDX revealed formation processes of microbial pyrite. In sludge(0-2.5cm depth) numerous diatoms(coscinodiscus nitidus) fom several framboidal pyrite(5μm diameter) inside cell. The framboidal pyrite are coated by thin film compose of Fe and S that is the almost same composition as pyrite. The BSI image shows slightly weak dense on the surface of film suggesting presence of organics. Chemical composition of normal diatom cell is almost pure Si. On the other hand, The diatom forming pyrite shows elementary differences between girdle and valve. Chemistory of the girdle shows Fe and S elements indicating substitution of Si. Quantity of Fe nad S increases outside to inside of girdle. The formation process of framboidal pyrite inside cell is as follows: The first step is formation of spherical FeS mineral(pyrrhotite), next step is a mixture of pyrite and pyrrhotite by adding S and dehydration. Then The mixture makes a rough framboid. Hexahedron and pentagonal dodecahedron are The characteristic crystal habits of framboidal pyrite in diatom. Some framboidal pyrite coated by thin film of clays with organics. dozens of framboid aggregate form a ball 50μm in diameter. Formation of framboidal pyrite in diatom should be initially controlled by organics of biofilms.
1993-05-25