XAS study of Fe mineralogy in a chronosequence of soil clays formed in basaltic cinders

• Published in: Clays and clay minerals Vol. 58; no. 6; pp. 772 - 782
• Main Authors: Baker, Leslie L, Strawn, Daniel G, Vaughan, Karen L, McDaniel, Paul A
• Format: Journal Article
• Language: English
• Published: Cham Clay Minerals Society 01.12.2010; The Clay Minerals Society; Springer International Publishing
• Subjects: basaltic composition; Biogeosciences; Butte County Idaho; chemical weathering; cinder cones; citrate-bicarbonate-dithionite method; clay mineralogy; clay minerals; Craters of the Moon National Monument; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Exact sciences and technology; Fe Mineralogy; Ferrihydrite; Geochemistry; Idaho; Inferno Cone Quadrangle; Medicinal Chemistry; mineral composition; Mineralogy; Nanoscale Science and Technology; oxides; rock, sediment, soil; sed rocks, sediments; Sedimentary petrology; sheet silicates; Silicates; Smectite; Soil Science & Conservation; soils; spectra; United States; volcanic features; Weathering; X-ray spectra; Xafs; XAFS spectra; Craters of the Moon; United States; Cascade Range; Weathering; Ferrihydrite; Smectite; XAFS; Fe mineralogy; minerals; oxalates; spectra; oxides; fine-grained materials; X-rays; ammonium; mineralogy; arid environment; North America; clay; cuttings; ferrihydrite; spectroscopy; sheet silicates; silicates; soils; clastic rocks; synchrotrons; absorption; dissolution; weathering; crystallinity; organic minerals; extraction; smectite; speciation; hydroxides; sedimentary rocks; secondary minerals; materials; clay minerals; frame structure
• ISSN: 0009-8604; 1552-8367
• DOI: 10.1346/CCMN.2010.0580605

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-bicarbonate-dithionite (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.