Variability of Chelyabinsk meteoroid stones studied by Mössbauer spectroscopy and X-ray diffraction.

The meter-scale variations of material properties of the 20-m sized Chelyabinsk meteoroid are critical for understanding why the meteoroid fragmented the way it did and caused the devastating airburst that sent over 1600 people to the hospital for treatment of glass cuts and minor injuries on February 15, 2013. From a range of differently looking unweathered meteorite fragments that were recovered shortly after the event, these material differences were probed by means of optical and scanning electron microscopy, X-ray diffraction (XRD), and the high velocity resolution Mössbauer spectroscopy. All main and some minor iron-bearing phases were identified on the basis of XRD data and Mössbauer spectra. The Fe2+ partitioning between the M1 and M2 sites in silicate phases was determined independently using XRD and Mössbauer data. Different meteorite fragments show a range of 570-1180 K in the temperature of the Fe2+ and Mg2+ equilibrium distribution between the M1 and M2 sites in olivine, while that in orthopyroxene falls in the range 870-1180 K (these ranges were estimated using both techniques). This fact points out a slightly different thermal history of these minerals before they accumulated in different parts of the Chelyabinsk meteoroid. The Chelyabinsk meteoroid is a fragmental breccia from materials formed at different depths in their parent body, or from materials that experienced different annealing temperatures in impacts. In addition, the fusion crust from two fragments, studied by XRD and Mössbauer spectroscopy, experienced a different thermal history during entry, suggesting that the fragment with mixed light and dark lithologies was located deeper inside the initial meteoroid than the fragment with only light lithology, or fragmented less readily.

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.