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Title: REDUCTION OF FE(III) IN GRIFFITHITE

Author
item KOMADEL, PETER - SLOVAK ACADEMY OF SCIENCE
item MADEJOVA, JANA - SLOVAK ACADEMY OF SCIENCE
item Laird, David
item XIA, Y - UNIV OF IL, DNR
item STUCKI, JOSEPH - UNIV OF IL, DNR

Submitted to: Clay International Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 9/14/2001
Publication Date: 9/14/2001
Citation: KOMADEL, P., MADEJOVA, J., LAIRD, D.A., XIA, Y., STUCKI, J.W. REDUCTION OF FE(III) IN GRIFFITHITE. CLAY INTERNATIONAL CONFERENCE PROCEEDINGS. 2001. P. 20.

Interpretive Summary:

Technical Abstract: Griffithite is a trioctahedral smectite with dioctahedral domains, found in the <2 um fraction of weathered basic rock from Griffith Park, California, USA. The <2 um sample was further fractionated to separate fractions surprisingly differing in colour. The 0.2-2 um fraction was brown, very similar to the <2 um fraction, the 0.06-0.2 um fraction was dark reddish-brown, while the finest fraction was dark yellow. Crystalline admixtures (albite, calcite, quartz and maghemite) were concentrated in the 0.2-2 um fraction, while the finest fraction contained only trace amounts of other minerals. Griffithite is primarily an iron-rich saponite with negative charge located on the tetrahedral sheets, the structural formula is Li0.86 [Si6.67 Al1.33][Al0.09 Fe(lll) 1.48 Fe(ll) 0.15 Mg3.64 Mn0.07] O20 (OH)4. The octahedral occupancy is about 91%, and about 26% of the octahedra contain trivalent atoms imparting a net positive charge to the octahedral sheet. Medium levels of Fe(lll) reduction in griffithite, up to 60% of total Fe, can be achieved by adding solid sodium dithionite to clay dispersions in a citrate-bicarbonate buffer. By contrast >90% reduction of Fe(lll) to Fe(ll) is achieved in nontronites using the same method. The lower reducibility of Fe(lll) in griffithite relative to nontronites may be due to structural differences between griffithite and nontronites, such as a more negative tetrahedral charge and a positive octahedral charge.