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Crystal growth of illitic minerals in open systems

开放系统中伊利石矿物的晶体生长

基本信息

批准号：
06453003
负责人：
INOUE Atsuyuki
金额：
$ 4.74万
依托单位：
Chiba University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-06453003/
关键词：
Illite Open system Crystal growth Crystal size distribution Kaolinite Hydrothermal system Weathering Ostwald's step rule 熱小変質カオリン混合層粘土鉱物

项目摘要

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.

本研究旨在从晶体生长和地球化学角度阐明天然开放体系下伊利石及相关矿物的形成机制。（1）利用XRD和TEM研究了水热环境下蒙脱石转化为伊利石过程中伊利石的生长机理，结果表明，伊利石的形成是通过前驱体溶解和新相的析出和生长实现的。新相的生长遵循螺旋生长机制。换句话说，热液环境是具有相对高的温度梯度和低岩/水比的系统的代表。在这样的系统中，伊利石的晶体尺寸分布的特点是由一个稳态的对数正态分布独立于不同的时间，结构和位置。生长伊利石晶体的习性变化可以从具有相对高的岩/水比的系统中区分出来。(2)通过对北海道大沼火山口湖悬浮液的XRD、TEM和溶液饱和指数的研究，发现高岭石在悬浮液中原位生长。在TEM和AFM下，高岭石的（001）面上看不到生长螺旋，但小晶体的聚结聚集体是特征。结果表明，高岭石晶体可能是在大沼对流流体循环系统中以二维生长机制和晶体聚结方式生长的。(3)风化作用中的反应系列，水铝英石 * 埃洛石 * 高岭石，是遵循奥斯特瓦尔德阶梯规则的天然矿物反应的代表。反应系列可以描述为连续溶解和沉淀的不太稳定和更稳定的相，以及在蒙脱石 * 伊利石反应系列。考虑到各矿物溶解度的尺寸依赖性，半定量地模拟了风化作用中的反应路径。