1996 Fiscal Year Final Research Report Summary
Crystal growth of illitic minerals in open systems
| Project/Area Number |
06453003
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Petrology/Mineralogy/Science of ore deposit
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| Research Institution | Chiba University |
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Principal Investigator |
INOUE Atsuyuki Chiba University, Faculty of Sci., Professor, 理学部, 教授 (30150270)
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| Co-Investigator(Kenkyū-buntansha) |
FURUKAWA Noboru Chiba University, Faculty of Sci., Assistant, 理学部, 助手 (40251194)
NISHIDA Takashi Chiba University, Faculty of Sci., Professor, 理学部, 教授 (40012405)
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| Project Period (FY) |
1994 – 1996
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| Keywords | Illite / Open system / Crystal growth / Crystal size distribution / Kaolinite / Hydrothermal system / Weathering / Ostwald's step rule |
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| Research Abstract |
The purpose of this study is to clarify the formation mechanism of illite and related minerals under natural open systems from crystal growth and geochemical viewpoints. The following results were obtained during the term of project :
(1) Growth mechanism of illite during the smectite-to-illite conversion in hydrothermal environments was studied by means of XRD and TEM.These studies indicated that illite is formed via dissolution of precursors and precipitation and growth of new phase. The growth of new phases is donimated by spiral growth mechanism. The hydrothermal environments, in other words, is representative of a system with relatively high temperature gradient and low rock/water ratio. In such systems the crystal size distribution of illite is characterized by a steady-state log-normal distribution independent of different times, structures, and locations. The habit change of growing illite crystals can be distinguishable from those in systems with relatively high rock/water ratios.
(2) It was found that kaolinite is in-situ growing in the suspension of Ohyunuma crater lake, Hokkaido, based on studies of XRD,TEM,and saturation index of solution. Growth spirals were not visible on the (001) face of kaolinite under TEM and AFM but coalescent aggregates of small crystals were characteristic. It suggests that the kaolinite crystals may be growing by 2-dimensional growth mechanism and crystal-coalescence under the convectional fluid circulation system of Ohyunuma.
(3) A reaction series, allophane * halloysite * kaolinite, in weathering is representative of a natural mineral reaction following to the Ostwald's step rule. The reaction series can be described by consecutive dissolution and precipitation of less stable and more stable phases as well as in smectite * illite reaction series. The reaction path in weathering was simulated semiquantitatively taking into account of the size-dependence of solubility of each minerals.
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