Clay Science
Online ISSN : 2186-3555
Print ISSN : 0009-8574
ISSN-L : 0009-8574
Paper
STRUCTURAL AND COMPOSITIONAL VARIANCES IN ‘HIDROBIOTITE’ SAMPLE FROM PALABORA, SOUTH AFRICA
Ryosuke Kikuchi Toshihiro Kogure
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JOURNAL FREE ACCESS

2018 Volume 22 Issue 2 Pages 39-52

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Abstract

A new reference sample of “hydrobiotite” mined at Palabora, the Republic of South Africa distributed by the Clay Science Society of Japan (CSSJ), was characterized by XRD, SEM, Mӧssbauer spectroscopy and TG-DTA. The XRD indicated that the sample was predominantly composed of the relatively regular interstratification of biotite- and vermiculite-layers, but segregated packets of vermiculite- and biotite-layers also existed, respectively. Diopside (Di75Hd25–Di80Hd20), wollastonite, apatite and titanite, were identified as impurity minerals. Mӧssbauer spectroscopy indicated that ∼83% of iron was ferric on average. Chemical compositions, especially the amount of K, were significantly varied among individual grains, while the compositional variance inside each grain was relatively small. The TG-DTA showed two sharp endothermic reactions at around 100 and 230°C, possibly corresponding to the two stages of dehydration of the interlayer region of the vermiculite-layer. In the range from 300 to 800°C, a gentle weight loss (about 2.5 wt%) was observed, corresponding to the dehydroxylation and/or the slow dehydration of water molecules tenaciously held in the interlayer. The total weight loss from 85 to 800°C was ∼7.0%. One-dimensional XRD profile simulation for mixed-layer structure was attempted for quantitative characterization of the mixed layer structure. At least four different stacking sequences were suggested for the major diffraction peaks; two types of relatively regular interstratified biotite- and vermiculite-layers (49.7% and 18.8% of the total number of layers), a biotite-layer rich stacking sequence (29.8%) and an almost pure vermiculite-layer stacking sequence (1.7%).

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© 2018 The Clay Science Society of Japan
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