An in situ study of thermal expansion of polymorphic phases of coarse-crystalline and nanocrystalline silver sulfide - monoclinic acanthite α-Ag2S and cubic argentite β-Ag2S - has been carried out for the first time using the high-temperature X-ray diffraction method. The temperature dependencies of the unit cell parameters of acanthite and argentite in the interval of 300-623 K have been determined, and the thermal expansion coefficients of acanthite and argentite have been found. It is shown that the observed difference in the thermal expansion coefficients for nano- and coarse-crystalline acanthite is due to the small particle size of nanocrystalline silver sulfide leading to the growth of anharmonicity of atomic vibrations. It is established by differential thermal analysis that a reversible polymorphic acanthite-argentite phase transformation takes place at ∼449-450 K and the phase transformation enthalpy is equal to ∼3.7-3.9 kJ mol(-1).

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We studied the interior and the fusion crust of the recently recovered Ozerki L6 meteorite using optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy, X-ray diffraction (XRD), magnetization measurements, and M€ ossbauer spectroscopy. The phase composition of the interior and of the fusion crust was determined by means of SEM, XRD, and M€ ossbauer spectroscopy. The unit cell parameters for silicate crystals were evaluated from the X-ray diffractograms and were found the same for the interior and the fusion crust. Magnetization measurements revealed a decrease of the saturation magnetic moment in the fusion crust due to a decrease of Fe-Ni-Co alloy content. Both XRD and M€ ossbauer spectroscopy show the presence of magnesioferrite in the fusion crust. The temperatures of cation equilibrium distribution between the M1 and M2 sites in silicates calculated using the data obtained from XRD and M€ ossbauer spectroscopy appeared to be in a good consistency: 553 and 479 K for olivine and 1213 and 1202 K for orthopyroxene.

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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 chondri te. 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 smal ler peak at 30 ±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 10 Be 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.