Clays and Clay Minerals, Vol. 58, No. 6, 772–782, 2010.
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Authors
Baker, Leslie L.
Strawn, Daniel G.
Vaughan, Karen L.
Mcdaniel, Paul A
Issue Date
2010
Type
Article
Language
Keywords
Periodicals , Geology , Fe mineralogy , Ferrihydrite , Smectite , Weathering , XAFS
Alternative Title
Xas Study Of Fe Mineralogy In A Chronosequence Of Soil Clays Formed In Basaltic Cinders
Abstract
The characterization of poorly crystalline minerals formed by weathering is difficult using conventional techniques. The objective of this study was to use cutting-edge spectroscopic techniques to characterize secondary Fe mineralogy in young soils formed in basaltic cinders in a cool, arid environment. The mineralogy of a chronosequence of soils formed on 2, 6, and 15 thousand year old basaltic cinders at Craters of the Moon National Monument (COM) was examined using synchrotron-based X-ray absorption fine structure (XAFS) spectroscopy in combination with selective extractions. Fe K-edge XAFS is useful for determining speciation in poorly crystalline materials such as young weathering products. Over 86% of Fe in the soil clay fractions was contained in poorly crystalline materials, mostly in the form of ferrihydrite, with the remainder in a poorly crystalline Fe-bearing smectite. The XAFS spectra suggest that ferrihydrite in the 15 ka soil clay is more resistant to ammonium oxalate (AOD) extraction than is ferrihydrite in the younger materials. Fe in the poorly crystalline smectite is subject to dissolution during citrate-bicarbonatedithionite (CBD) extraction. The results indicate that relatively few mineralogical changes occur in these soils within the millennial time frame and under the environmental conditions associated with this study. Although the secondary mineral suite remains similar in the soils of different ages, ferrihydrite crystallinity appears to increase with increasing soil age.
Description
gsccm58605-bak.pdf -- 443KB
Citation
Clays and Clay Minerals, Vol. 58, No. 6, 772–782, 2010.
Publisher
The Clay Minerals Society
License
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