A Mössbauer effect study of the Soledade meteorite

Abstract

We performed a Mössbauer spectroscopy study of the iron meteorite Soledade. This meteorite, which consists of a metallic matrix, is an octahedrite with polycrystalline troilite, cohenite, schreibersite and rhabdites as major constituents. A chemical analysis indicates 6.78 % Ni, 0.46% Co, besides traces of Cu, Cr, Ga, Ge, As, Sb, W, Re, Ir and Au. No traces of silicates have been found and no oxygen was detected. Iron is appearing in the austhenitic phase and alloyed with nickel. An analysis of the Mössbauer spectra at room temperature indicates that the Fe-Ni phase is homogeneously distributed in the matrix, although variations in the composition between different regions are observed.Since the early studies of the microstructure and chemical composition of meteorites the formation of magnetic phases has attracted the attention of metallurgists [1][2][3][4][5][6][7][8][9][10][11]. Most of the metallic specimens presented high contents of nickel and iron as major constituents, and thus the Fe-Ni alloys formed under such special conditions have been the subject of several investigations with a variety of experimental techniques. This is not an easy task considering the weathering process and the distribution of oxides in the metallic matrix, which in some cases varies in composition from one region to another. However, the complexity of the mechanism of formation of the alloys in meteorites, which can take cooling rates as long as 1 K/Ma, is an interesting subject, and its comprehension may shed some light on the metastability of alloys.The category of iron meteorites corresponds to about 5 % of the modern meteorite falls. In the study of Fe-Ni-bearing meteorites, there is a recent discussion about the formation of a low-moment Fe-rich γ phase which differs from the ordinary high-spin γ phase in the electronic structure and a lower lattice parameter, but has the same crystal structure, same degree of atomic order and same composition of ordinary taenite. In fact, this has been claimed to be a new mineral called antitaenite which is common in slowly cooled meteorites [12][13][14]. This low-spin phase is proposed to occur in a thin epitaxial intergrowth with tetrataenite (ferromagnetic atomically ordered FeNi). Actually, metastable precipitates of this low-spin phase in a matrix of high-spin Fe-Ni phase of the same controlled composition have been synthetically produced near the Invar composition (≈ 35 at% Ni).In this work we applied x-ray diffraction (XRD) and Mössbauer spectroscopy (MS) to study the iron-bearing phases detected in the iron meteorite called Soledade, which is a massive metallic block [15]. Although no one knows precisely when this specimen was found, it received the name of the locality from where it proceeded near the city of Passo Fundo in the state of Rio Grande do Sul in Brazil. The first studies indicate that this metallic meteorite is an octahedrite, with polycrystalline troilite, cohenite, schreibersite and rhabdites as major constituents. It consists of a solid block weighing 68 kg, with a...

Mössbauer study of Meridiani Planum, the first iron‐nickel meteorite found on the surface of Mars by the MER Opportunity

“…This finding is consistent with the presence of Ni in the α-Fe structure, as suggested by the in situ MER APXS analysis of the meteorite target and with the conclusion put forward by Morris et al (2006). It is also consistent with data for the ironnickel meteorite Soledade, which has a Ni concentration of 6.8 wt%, and for which a hyperfine field of 34.4 T at room temperature (Paduani et al 2005) was measured. This value is higher by about 1.4 T compared to the hyperfine field that is typical for α-Fe at room temperature, i.e., 33.0 T.…”

Comparative study of Aliskerovo, Anyujskij, Sikhote-Alin and Sterlitamak iron meteorites using Mössbauer spectroscopy

“…Therefore, it is not possible to reproduce extraterrestrial Fe-Ni-Co alloys in the terrestrial conditions while some features of meteorite metallic iron may be useful for new alloys development. Mössbauer spectroscopy is a useful tool for study iron meteorites (see, for instance, [2][3][4][5]). Therefore, we have applied Mössbauer spectroscopy to study some iron meteorites in order to evaluate the relationship of the hyperfine parameters and metal phases in meteorites with variations in Ni concentration [6,7].…”

Applications of Mössbauer Spectroscopy in Meteoritical and Planetary Science, Part II: Differentiated Meteorites, Moon, and Mars

“…A discussion ab questionable term "antitaenite" was already reported in Part I, Section 6.1 [1]. Mo the authors of [64], who also observed the paramagnetic singlet in the Mössbaue trum of Santa Catharina, determined the Ni content of 28 at.% for this compone corresponded to the well-known paramagnetic γ-Fe(Ni) phase (paramagnetic taen A comparison of the different areas of the coarse octahedrite Soledade IAB-Mössbauer spectroscopy was carried out in [71]. The Fe-Ni alloy contained about 6 Ni, indicating the α-Fe(Ni, Co) phase.…”

“…In co the surface spectrum mainly showed the presence of ferric compounds in the m and paramagnetic states. A comparison of the different areas of the coarse octahedrite Soledade IAB-MG by Mössbauer spectroscopy was carried out in [71]. The Fe-Ni alloy contained about 6.7 at.% Ni, indicating the α-Fe(Ni, Co) phase.…”