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Characterization of barren, granitic soils from the Nubian Desert (SW Egypt) by 57Fe Mössbauer spectroscopy

Hassan K. M., Gunnlaugsson H. P.

Mineralogia

2013

Vol. 44, iss. 1/2

39--50

57 Fe Mössbauer spectroscopy - a versatile technique involving the recoil-free, resonant absorption and emission of nuclear gamma (γ) rays by the iron-57 isotope in natural iron in solids - has been used to provide quantitative information about the mineral host, occupation sites and oxidation states of iron atoms in geological samples. This technique has been applied to the bulk chemistry of a barren soil (Soil A) derived from an aluminous-type granite and another barren soil (Soil B) derived from a sodic-type granite located ~ 100 kilometers apart in the Nubian Deseit in the currently hyper arid south-west of Egypt and which exhibit distinct chemical and mineral differences. The analyses indicate different mineral hosts for the iron in these samples, namely, vermiculite-chlorite plus some hematite in Soil A and hematite and goethite plus minor aegirines in Soil B. Each soil has distinct intensities of oxidized iron (89% for Soil A and 100% for Soil B) and these differences reflect changes in soil sources and processes.

Valences and site characteristics of iron in radioactive magmatic veins (Egypt): A Mössbauer and chemical study

Hassan K. M.

Mineralogia

2010

Vol. 41, iss. 1/2

23--33

Radioactive veins in shear zones of the El-Seboah granite in Egypt with anomalous concentrations of Nd, Ce, Zr, Y, Nb, Sm, Th and U were studied by petrographic microscopy, x-ray diffraction, 57Fe Mössbauer and wet chemical methods. The veins are composed essentially of quartz, aegirine-augite and minor K-feldspar ± α-iron oxide (hematite) ± γ-iron oxide hydroxide (goethite). They likely represent late-stage felsic melt that was quenched and devitrified at high temperature to yield crystals and crystallites, and then subjected to low temperature alteration during which most of the K feldspar transformed to kaolinite and opal. Mössbauer parameters of the samples indicate that the existing Fe-bearing minerals are primary, with appreciable ordering in the Fe sites. The bulk-sample iron (ΣFe) contents are extremely high (12.3-22.4%). The extent of oxidation of the Fe has been found to be 100% by Mössbauer spectroscopy and 95.36-99.69% by a chemical method. These conditions of Fe enrichment and strong oxidation suggest that the veins are extreme differentiates of granite magmas where high states of oxygen fugacity prevailed.

Local electronic and charge state of iron in FeTe2

Stanek J., Fornal P.

Nukleonika

2004

Vol. 49,suppl.3

63-65

From 57Fe Mössbauer spectrum of FeTe2 taken in high external magnetic field (B = 4.6 T), the sign of electric field gradient was determined as negative, with an asymmetry parameter of 0.2. A comparison of these data with results of calculation of the electric field gradient within point charge model suggests the lattice character of electric field gradient with some contribution from covalency effects. The effective magnetic field acting on 57Fe is less than the applied, which points out the diamagnetic Fe+2 state of iron. This "electronic state" is in a contradiction to Fe+3 "charge state" concluded from 125Te experiments on 3d transition metal ditellurides as well as from 57Fe quadrupole splitting and isomer shift.