Hydrothermal Experiments on Materials Corresponding to Fluor-hydroxyl Chrysotile [Mg&lt;sub&gt;6&lt;/sub&gt;Si&lt;sub&gt;4&lt;/sub&gt;O&lt;sub&gt;10&lt;/sub&gt;F&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;(OH)&lt;sub&gt;8-&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;

Masumi Ushio,Hajime Saito

doi:10.2109/jcersj1950.78.903_359

Abstract

Mixtures of SiO2 (amorphous), Mg(OH)2 (brucite) and MgSiF6⋅6H2O corresponding to the compositions [Mg6Si4O10Ex(OH)8-x] of different x values were treated hydrothermally at temperatures from 270 to 1000°C, under water pressures ranging from 100 to 1000 atm.The heat-treated samples were examined by an X-ray diffractometer and under a polarizing or electron microscopes.Treatment of the sample with x=1.5 at temperatures below 500°C formed chrysotile in coexistence with minor quantity of sellaite and talc. Talc and chondrodite were found to be the main crystalline phases between 500° and 580°C and coexisted with cristobalite between about 600° and 800°C. Above about 830°C, chondrodite, cristobalite and minor quantity of unidentfied minerals were observed.Treatment of the sample with x=3.0 at temperatures below about 400°C formed chrysotile, sellaite and minor quantity of unidentified minerals. At temperatures ranging from about 430 to 480°C, chondrodite was found to be a main crystalline phase and coexisted with crysotile, talc and minor quantity of unidentified minerals. Talc was formed, coexisting with chondrodite (or norbergite), cristobalite (or α-quartz) and minor quantity of unidentified minerals, at temperatures between about 500° and 800°C. Above about 900°C, chondrodite (or nordergite), cristobalite and minor quantity of unidentified minerals were obtained.Treatment of the sample with x=6.0 at temperatures below 420°C formed sellaite in coexistence with minor quantity of talc and chrysotile. Talc, sellaite and minor quantity of unidentified minerals were obtained between about 450 and 650°C. At temperatures between about 700° and 800°C, talc was a main crystalline phase and coexisted with chondrodite, norbergite and unidentified minerals.Treatment of the sample with x=8.0 at temperatures ranging from about 300 to 500°C formed sellaite in coexistence with minor quantity of chrysotile. Talc and sellaite, coexisted with cristobalite and chondrodite (?), were the main crystalline phases between about 550° and 800°C. Above about 850°C, cristobalite and norbergite were obtained.In the specimen of x=12, that is, [Mg6Si4O10F12] composition, sellaite and cristobalite (or α-quartz) were found in the specimen treated at temperatures between about 250°C and 800°C.Hydroxyl-chrysotile [Mg6Si4O10(OH)8] was an exception and any stability region of a single phase of fluor-hydroxyl chrysotile [Mg6Si4O10Fx(OH)8-x] did not exist, but fluorine ion in the specimen was inclined to react preferentially with magnesium ion to form sellaite.

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