Goethite Mossbauer spectra

Fig. 8.31 Left) In the Mossbauer spectrum taken in the Columbia Hills at a rock called Clovis the mineral goethite (GT) (a-FeOOH) could be identified. GT is a clear mineralogical evidence for aqueous processes on Mars. Right) The rock Clovis is made out of rather soft material as indicated by the electric drill-current when drilling the - - I cm deep hole seen in the picture. Drill fines are of brownish color. The pattern to the right of the drill hole was made by bmshing the dust off the surface by using the RAT...

The method produces ca. 5-6 g goethite of low crystallinity and a surface area of about 80 m /g. The crystals resemble goethites from various natural environments. An X-ray diffractogram is shown in Fig. 5-9, an EM photo in Fig. 5-10 and a Mossbauer spectrum in Fig. 5-11. An X-ray... 

Properties XRD pattern, Mossbauer spectrum available [1318]. PZC/IEP of hematite-goethite composite is presented in Table 3.468. 

Influence of Tetravalent Cations The influence of the Ti ion presence during the formation of goethite from ferric solution in an alkaline medium was investigated by Mossbauer spectroscopy and other techniques [246]. The presence of Ti " " ions partially suppressed the transformation of ferrihydrite to goethite and as a result a quadrupole doublet, corresponding to the low-crystalline phase, emerged in the Mossbauer spectrum. 

Fig. 3.38 Mossbauer spectrum at RT and at 80 K of a hematite-rich sample containing hematite and goethite...

Another example concerns the Mossbauer measurement of iron-containing nodules in a planosol from the S-W Ethiopian highlands [270]. The RT Mossbauer spectrum of the nodules in the vertic horizon as well as that of the accumulated nodules consists of a single doublet at RT, which converts partly into a goethite sextet at 80 K (Fig. 3.43). The remaining Fe " doublet with a quadrupole splitting of 0.60 mm/s might be attributed to ferrihydrite. 

Figure 4.69 Mossbauer spectrum of sample 3.1 A red) and B dark red) sites in magnetite, as weU as goethite pink) and hydroxide green) were identified...

The many Mossbauer investigations of the spectra taken by the MERs on soils and rocks along their pathways showed olivines and pyroxenes as the main silicates [294—296]. Most interesting was the obvious observation of a jarosite spectrum, inferring the former presence of water on Mars [297]. This was also corroborated by the identification of goethite in the spectra from some locations [298]. 

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