Ammonioalunite, ammoniojarosite and their solid-solution series found on a burning coal dump at Czerwionka, Upper Silesian Coal Basin, Poland, were examined using powder X-ray diffraction, electron probe microanalysis, inductively coupled plasma mass spectrometry, infrared spectroscopy and thermal analysis methods. The minerals occur as yellow, fine-grained crusts and botryoidal masses in the outer part of a sulphate crust found ∼1 m below the surface. The crust is composed mainly of godovikovite and tschermigite that formed by interaction of sour fire gases or solutions and waste materials beneath the surface of the burning coal dump at temperatures of at least 80—100°C. The crystals often reveal oscillatory zoning due to different Al and Fe contents in thin bands, from near end-members to extensive solid solutions. Our analyses suggest the existence in nature of a complete solid solution between ammonioalunite and ammoniojarosite. They also carry essential amounts of chlorine.

X-ray diffraction studies of crystals under pressure and quantitative experimental charge density analysis are among the most demanding types of crystallographic research. A successful feasibility study of the electron density in the mineral grossular under 1 GPa pressure conducted at the CRISTAL beamline at the SOLEIL synchrotron is presented in this work. A single crystal was placed in a diamond anvil cell, but owing to its special design (wide opening angle), short synchrotron wavelength and the high symmetry of the crystal, data with high completeness and high resolution were collected. This allowed refinement of a full multipole model of experimental electron distribution. Results are consistent with the benchmark measurement conducted without a diamond-anvil cell and also with the literature describing investigations of similar structures. Results of theoretical calculations of electron density distribution on the basis of dynamic structure factors mimic experimental findings very well. Such studies allow for laboratory simulations of processes which take place in the Earth's mantle.

The results of a complex investigation of the sulphate and arsenate assemblages forming in the weathering zone of selected ore deposits in the Sudetes are presented. The development of the weathering zone has been characterised in the polymetallic ore deposits at Miedzianka-Ciechanowice and Radzimowice, and the pyrite deposit at Wieściszowice, which differ in the chemical compositions of the ore and barren minerals and the hydrological conditions. Secondary sulphate and arsenate mineral assemblages vary significantly among the ore deposits under study. Their crystallization is discussed, taking into consideration the stability of particular minerals and the paths of their transformation. It is shown that these minerals have great potential as indicators of weathering processes. A significant role for microorganisms in the formation of the weathering zone of the ore deposits under study is also proven.

Pressure is well known to dramatically alter physical properties and chemical behaviour of materials, much of which is due to the changes in chemical bonding that accompany compression. Though it is relatively easy to comprehend this correlation in the discontinuous compression regime, where phase transformations take place, understanding of the more subtle continuous compression effects is a far greater challenge, requiring insight into the finest details of electron density redistribution. In this study, a detailed examination of quantitative electron density redistribution in the mineral langbeinite was conducted at high pressure. Langbeinite is a potassium magnesium sulfate mineral with the chemical formula [K₂Mg₂(SO₄)₃], and crystallizes in the isometric tetartoidal (cubic) system. The mineral is an ore of potassium, occurs in marine evaporite deposits in association with carnallite, halite and sylvite, and gives its name to the langbeinites, a family of substances with the same cubic structure, a tetrahedral anion, and large and small cations. Single-crystal X-ray diffraction data for langbeinite have been collected at ambient pressure and at 1 GPa using a combination of in-house and synchrotron techniques. Experiments were complemented by theoretical calculations within the pressure range up to 40 GPa. On the basis of changes in structural and thermal parameters, all ions in the langbeinite structure can be grouped into `soft' (potassium cations and oxygens) and `hard' (sulfur and magnesium). This analysis emphasizes the importance of atomic basins as a convenient tool to analyse the redistribution of electron density under external stimuli such as pressure or temperature. Gradual reduction of completeness of experimental data accompanying compression did not significantly reduce the quality of structural, electronic and thermal parameters obtained in experimental quantitative charge density analysis.

Atom location by channeling-enhanced microanalysis (ALCHEMI) was used to determine the occupancy of Al atoms in the T_1o site (t_1o) of alkali feldspar. Building on the method demonstrated by previous research, analytical electron microscopy proves to be a viable technique for fully characterizing the Al-Si ordering state in the feldspar framework. We applied this method to orthoclase from Itrongay, Madagascar, and to its heated counterpart. Our preliminary results give 0.74 and 0.37 as 2t₁ (=t_1o + t_1m) and t_1o, respectively, for the original orthoclase, vs. 0.54 and 0.28 for heated orthoclase. Single-crystal X-ray diffraction experiments have been performed, and the results agree with our ALCHEMI measurements. This new method promises to help resolve some complex issues relating ordering paths, for example, twinning in feldspars and domain intergrowth in plagioclase.