L. Vistisen

Iron-containing weathering products of basalt in a cold, dry climate

Two different microenvironments for secondary iron mineral formation in a basaltic stone exposed to weathering in the cold, dry climate at the top of a nunatak in Greenland have been investigated. At the upper, exposed surface a red stained rind (varnish) has formed, and within a crack, a loose, reddish-brown material and a greenish coloured material were found. The weathering products were identified by 57Fe Mossbauer spectroscopy, X-ray diffraction and infrared spectroscopy. The reddish stain on the exposed surface consists of hematite. In contrast, the reddish-brown material from the crack contains goethite and magnetite/maghemite, but no hematite could be detected. Nontronite is the main mineral in the greenish material. The conditions determining the neoformation of minerals in the two environments are briefly discussed.

Mössbauer spectroscopy on the surface of Mars. Why

A Mössbauer spectrometer is included in the preliminary payload of a rover to be placed on the surface of Mars in the Soviet mission to the planct in 1996/1,2/. In counection with the American planctary program it has also been suggested to construct a Mössbauer spectrometer to be landed on Mars /3, 4/. The objective is to study the iron compounds of the Martian soil and rocks by backscattering Mössbauer spectroscopy. The paper describes the significance of the element iron in the study of the evolution of the planetary system and what we might expect to learn from Mössbauer spectroscopy of the surface materials of Mars. The study of Mars is expected to expand substantially in the coming decades, probably culminating with a manned flight to the planet. The international Mössbauer community may contribute significantly to the preparation of these events.

Oxidation state of iron in SNC meteorites as studied by Mössbauer spectroscopy

Mossbauer investigations of three meteorites of the type SNC-achondrites are reported. The results are compared with Mossbauer spectra of other meteorites, and selected terrestrial and lunar rocks. Through the oxidation state of iron in the pyroxenes and magnetic oxides studied, the work confirms that the mantle of the Earth is highly oxidized compared with the mantle of asteroidal bodies and lunar basalts. The investigations show that at least one of the SNC meteorites (Nakhla) comes from a highly oxidized parent body, believed to be the planet Mars. Based on the results obtained, a somewhat general conclusion about the oxidation state of iron in planetary bodies is proposed.

Mössbauer spectroscopy showing large-scale inhomogeneity in the presumed martian meteorite Zagami

A group of nine achondritic meteorites, the SNC-meteorites, are believed to be rocks from the planet Mars. With the planned exploration of Mars in mind, perhaps including in situ Mossbauer spectroscopy, the study of the SNC-meteorites takes on a specific significance. We have performed Mossbauer spectroscopy of specimens from one of these meteorites, Zagami. Surprisingly, the Mossbauer spectra of two separate samples from Zagami are very different. One of the samples shows no olivine, in agreement with the description of the meteorite Zagami in the literature. The other sample shows that about 23% of the iron is placed in olivine, and X-ray diffraction analysis confirms the existence of olivine as a major component in this sample. We are thus forced to conclude that the meteorite Zagami is inhomogeneous on a macroscopic scale. This result has evidently implications for the understanding of the igneous rocks on Mars, and thus for the interpretation of their Mossbauer spectra.

Titanium and the magnetic phase on Mars

The significance of the element titanium for the study of the magnetic mineral in the surface dust of Mars is described.

Iron-Nickel Alloys in a Taenite Lamella from the Iron Meteorite Cape York as Measured by Conversion Electron Mossbauer Spectroscopy

Taenite lamellae from iron meteorites consist of different iron-nickel phases, e.g., a paramagnetic, disordered f.c.c. phase ( 25% Ni) and a ferromagnetic, ordered FeNi (50%-50%) phase. By reflection Mossbauer spectroscopy using a conversion electron counter it is possible to study thin surface layers (~ 1000 A) of the lamellae. Information on the distribution of phases in a taenite lamella from the iron meteorite Cape York has been obtained by combining etching and conversion electron Mossbauer spectroscopy.

A study of Ni-rich iron meteorites

Samples from the two Ni-rich iron meteorites Santa Catharina and Twin City have been investigated by conventional Mössbauer spectroscopy and by conversion electron Mössbauer spectroscopy. The spectra obtained show that the major components of these two meteorites are an ordered FeNi (∼50%, ∼50%) phase and a paramagnetic Fe−Ni phase with ≤28% Ni.

ARE PHOBOS AND DEIMOS CARBONACEOUS CHONDRITES? MÖSSBAUER SPECTROSCOPY ON CARBONACEOUS CHONDRITES AND THEIR RELATION TO THE MARTIAN MOONS

ABSTRACT The Martian moons Phobos and Deimos are relatively small (r ∼ 104 m) irregularly shaped objects that represent a large class of small Solar System Bodies. Based on spectral reflectance measurements and comparison with meteorites the Martian moons are believed to be of Carbonaceous Chondrite composition /1/. The Carbonaceous Chondrites are characterized by a very high average oxidation state of the iron in them compared to that of all other types of meteorites. By use of Mossbauer Spectroscopy Carbonaceous Chondrites of the classes CI, CM, CV and CO are easily distinguished from each other and from other classes of meteorites. The possibility of identifying the Martian moons as distinct types of Carbonaceous Chondrites based on Mossbauer spectra of the surface is investigated.

MÖSSBAUER SPECTROSCOPY OF SNC METEORITES

ABSTRACT The achondrite Nakhla, belonging to the group of SNC meteorites, is more oxidized than the ordinary achondrites, e.g. Nakhla contains titanomagnetite (≈2%). Besides the Fe3+ in the titanomagnetite, Nakhla includes other compounds carrying Fe3+. By means of Mossbauer spectroscopy we demonstrate that in some of the pyroxenes separated from Nakhla the Fe3+ is distributed throughout the crystals, i.e. the oxidation of the pyroxenes in Nakhla is not only a surface phenomenon.