Smectite formation in rhyolitic obsidian as inferred by microscopic (SEM-TEM-AEM) investigation

被引:26
作者
Fiore, S
Huertas, FJ
Huertas, F
Linares, J
机构
[1] CNR, Ist Ric Argille, I-85050 Tito, PZ, Italy
[2] CSIC, Estac Expt Zaidin, Dept Ciencias Tierra & Quim Ambiental, E-18008 Granada, Spain
关键词
obsidian; alteration; Fe-smectite; Mg-smectite; mechanism of formation; electron microscopy;
D O I
10.1180/0009855013640004
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Experimental alteration of a rhyolitic obsidian by solutions containing variable concentrations of Mg was carried out at 100, 150 and 200degreesC, for 30, 60 and 90 days, to investigate the mechanism of smectite formation. The smectite exhibits two distinct morphologies: (1) small flakes (aggregates of a few crystals); and (2) large flakes (massive groups). The small flakes are the earlier alteration products. Both morphological types have distinct chemical compositions: the smallest laminae are dioctahedral and contain more Fe, whereas the particles from the rose-shaped aggregates contain Mg and are trioctahedral, Intermediate compositions have been observed between the extreme compositions. It is suggested that the two morphologies are the result of two distinct genetic processes: (1) the small flakes (Fe-rich smectite) form by solid state rearrangements of the hydrated external layer of glass and/or via the formation of domains within the glass; (2) the rose-shaped aggregates (Mg-rich smectite) form by precipitation from solution.
引用
收藏
页码:489 / 500
页数:12
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