Oriented precipitate complexes in iron-rich olivines produced experimentally in aqueous oxidizing environment |
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| Authors: | Kazuake Iishi Kazunobu Torigoe Xiaojun Han |
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| Institution: | (1) Department of Earth Sciences, Faculty of Science, Yamaguchi University, Yoshida, Yamaguchi 753, Japan, Fax:+81 839 33 5742, JP |
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| Abstract: | Iron-rich olivines (Fa100∼Fa70Fo30) experimentally altered in alkaline and acidic aqueous oxidizing environment were examined in transmission electron microscope
to determine the precipitate phases and their crystallographic relationships to the host. The planar zones consist of precipitates
of laihunite and hematite in alkaline aqueous oxidizing environment while hematite and amorphous silica in acidic aqueous
oxidizing environment. The directions of planar zones produced in alkaline aqueous oxidizing environment are parallel to (100)∼(001)
of olivine dependent on the composition of the host olivines, while those produced in acidic aqueous oxidizing environment
are always parallel to (001) of olivine independent from the composition of the host olivine. These differences are interpreted
by the dissolution kinetics of olivine.
The present experimental results explain why the planar zones found in oxidized iron-rich olivines in carbonaceous chondrite
are parallel to (100) of olivine while those in terrestrial olivines are parallel to (001) of olivine. That is, the difference
is attributed to the pH of the alteration environment.
Received: August 19, 1996 / Revised, accepted: February 14, 1997 |
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