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Spectroscopic and Geochemical Analyses of Ferrihydrite from Hydrothermal Springs in Iceland and Applications to MarsFerrihydrite samples were collected from a thermal spring and a cold stream in the Landmannalaugar region of Iceland. Chemical and spectroscopic analyses have been performed on the air-dried and fine-grained fractions of these samples. The ferrihydrite from the cold stream is a pure sample, containing small amounts of Ca, P and Si, which do not form minerals detectable with X-ray diffraction (XRD) or reflectance and transmittance spectroscopy. The ferrihydrite from the thermal pool is a less pure sample, containing larger amounts of amorphous Si and P. The XRD and spectral features for this sample are also consistent with a less crystalline structure. Some of the Si is incorporated in the structure of the ferrihydrite. The Ca, P and possibly some of the Si may be biogenic. The spectral character of these Icelandic ferrihydrites is compared with those of synthetic ferrihydrites and other iron oxide/oxyhydroxide minerals. Ferrihydrite is characterized by a broad Fe3+ excitation band near 0.92 microns (approx. 10900/cm) and a strong Fe-O absorption feature near 475/cm (approx. 21 microns) in transmittance spectra. Multiple bands due to H2O and OH are also present for ferrihydrite. Natural ferrihydrites frequently exhibit a band near 950-1050/cm (approx. 10 microns) that is typically not observed for synthetic ferrihydrites and may be due to some Si in the structure. An additional pair of spectral bands near 1400 and 1500/cm (approx. 7 microns) are characteristic of pure ferrihydrites from natural and synthetic sources. Hydrothermal springs may have been present at one time on Mars in association with volcanic activity. Ferrihydrite formation in such an environment may have contributed to the ferric oxide-rich surface material on Mars.
Document ID
20010091028
Acquisition Source
Ames Research Center
Document Type
Preprint (Draft being sent to journal)
Authors
Bishop, Janice
(Search for Extraterrestrial Intelligence Inst. CA United States)
Murad, E.
(Bavarian Geological Survey Germany)
DeVincenzi, Donald L.
Date Acquired
August 20, 2013
Publication Date
January 10, 2001
Subject Category
Inorganic, Organic And Physical Chemistry
Funding Number(s)
PROJECT: RTOP 896-50-21-01
CONTRACT_GRANT: NCC2-1100
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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