A.A. Maksimova

Comparison of iron-bearing minerals in ordinary chondrites from H, L and LL groups using Mössbauer spectroscopy with a high velocity resolution.

Ordinary chondrites from H, L and LL groups were studied using Mössbauer spectroscopy with a high velocity resolution. Mössbauer parameters of spectral components were obtained using new fitting model excluding the effect of previous misfits of troilite component. Obtained parameters were related to corresponding iron-bearing minerals in ordinary chondrites. The differences of these minerals content as well as small differences in the hyperfine parameters of the same iron-bearing minerals were revealed for different meteorites. The temperatures of equilibrium cations distribution in silicates were estimated and suitable parameters for classification of H, L and LL chondrites were supposed using Mössbauer parameters.

Study of Chelyabinsk LL5 meteorite fragment with a light lithology and its fusion crust using Mössbauer spectroscopy with a high velocity resolution

Study of Chelyabinsk LL5 ordinary chondrite fragment with a light lithology and its fusion crust, fallen on February 15, 2013, in Russian Federation, was carried out using Mossbauer spectroscopy with a high velocity resolution. The Mossbauer spectra of the internal matter and fusion crust were fitted and all components were related to iron-bearing phases such as olivine, pyroxene, troilite, Fe-Ni-Co alloy, and chromite in the internal matter and olivine, pyroxene, troilite, Fe-Ni-Co alloy, and magnesioferrite in the fusion crust. A comparison of the content of different phases in the internal matter and in the fusion crust of this fragment showed that ferric compounds resulted from olivine, pyroxene, and troilite combustion in the atmosphere.

Characterization of Northwest Africa 6286 and 7857 ordinary chondrites using X-ray diffraction, magnetization measurements and Mössbauer spectroscopy

Northwest Africa (NWA) 6286 and 7857 meteorites were studied in detail by using optical microscopy, scanning electron microscopy with energy dispersion spectroscopy, X-ray diffraction, magnetization measurements and 57Fe Mössbauer spectroscopy with a high velocity resolution. The main and the minor iron-bearing phases were identified in both meteorites. The unit cell parameters as well as Fe2+ and Mg2+ cation distribution were determined for the M1 and M2 sites in silicate microcrystals. Saturation magnetic moments were obtained for both meteorites. Mössbauer parameters for the main and the minor iron-bearing microcrystals were estimated and compared for NWA 6286 and NWA 7857 LL6 ordinary chondrites. The Fe2+ and Mg2+ cation partitioning, distribution coefficient and temperature of cation equilibrium distribution were estimated for silicate microcrystals using X-ray diffraction and Mössbauer spectroscopy.

Annama H chondrite—Mineralogy, physical properties, cosmic ray exposure, and parent body history

The fall of the Annama meteorite occurred early morning (local time) on April 19, 2014 on the Kola Peninsula (Russia). Based on mineralogy and physical properties, Annama is a typical H chondrite. It has a high Ar-Ar age of 4.4 Ga. Its cosmic ray exposure history is atypical as it is not part of the large group of H chondrites with a prominent 7 - 8 Ma peak in the exposure age histograms. Instead, its exposure age is within uncertainty of a smaller peak at 30 \pm 4 Ma. The results from short-lived radionuclides are compatible with an atmosperic pre-entry radius of 30 - 40 cm. However, based on noble gas and cosmogenic radionuclide data, Annama must have been part of a larger body (radius >65 cm) for a large part of its cosmic ray exposure history. The 10Be concentration indicates a recent (3 - 5 Ma) breakup which may be responsible for the Annama parent body size reduction to 30 - 35 cm pre-entry radius.

The Fe 2+ occupancies in the silicates M1 and M2 sites in Chelyabinsk LL5 meteorite determined using XRD and Mössbauer spectroscopy

Study of four Chelyabinsk LL5 ordinary chondrite fragments with different lithology was carried out using X-ray diffraction and Mössbauer spectroscopy with a high velocity resolution. The Fe2+ occupancies of the M1 and M2 sites in olivine, orthopyroxene, and clinopyroxene determined using X-ray diffraction and Mössbauer spectroscopy were compared. Distribution coefficients KD and the temperatures of cations equilibrium distribution Teq in the olivine and orthopyroxene were evaluated.

Revealing of the minor iron-bearing phases in the Mössbauer spectra of Chelyabinsk LL5 ordinary chondrite fragments

A detailed analysis of two fragments of Chelyabinsk LL5 ordinary chondrite using scanning electron microscopy with energy dispersion spectroscopy, X-ray diffraction and 57Fe Mossbauer spectroscopy with a high velocity resolution was carried out. Chemical analysis demonstrated the presence of the minor iron-bearing phases such as chromite, hercynite, ilmenite, α-Fe(Ni, Co), α2-Fe(Ni, Co), γ-Fe(Ni, Co) in addition to the main iron-bearing phases (olivine, orthopyroxene and troilite). These minor components were also revealed in the XRD and Mossbauer spectra of the two fragments of Chelyabinsk LL5 meteorite.