Corundum is an important oxide mineral which can contain low amounts of hydrogen-bearing structural defects. These defects are observed by infrared spectroscopy, but their atomic-scale geometry is still uncertain. Here, a theoretical approach makes it possible to relate most of the observed infrared bands to specific atomic configurations, highlighting the key role of other chemical impurities and defect clustering in the high-temperature incorporation of hydrogen in corundum.

The structural response of the NH₄⁺ molecule to temperature and pressure changes is studied in ammonium phengite. The symmetry of the molecule is lowered by increasing P or decreasing T; the type and mechanism of this lowered symmetry is different in both cases. Devolatilisation (NH₄⁺ and OH loss) of ammonium phengite is studied as well. This study confirms the wide stability range of phengite and its volatiles and thus has important implications for N and H recycling into the deep Earth.

Wumuite, ideally KAl_0.33W_2.67O₉ with a hexagonal tungsten bronze (HTB)-type structure, is another new mineral containing potassium and tungsten found in the Pan–Xi region in China after tewite was discovered. In this study, artificial synthetic experiments have been conducted to explore the formation process of wumuite and tewite. Wumuite was speculated to be formed by a metasomatic reaction between W-rich hydrothermal fluids and the potassium feldspar in the monzonite.

The atomic-scale geometry of hydrous defects in diopside is still imperfectly known despite their contribution to the Earth's water cycle. Their OH-stretching vibrations lead to a variety of infrared absorption bands. Low-temperature infrared spectroscopy makes it possible to resolve additional bands in the spectra of gem-quality natural samples. Theoretical results obtained at the density functional theory level support the assignment of the observed bands to specific atomic-scale models.

We analysed apatite–allanite/epidote coronae around monazite and xenotime in deformed Permian pegmatites from the Austroalpine basement. Microscopy, chemical analysis and EBSD showed that these coronae formed by dissolution–precipitation processes during deformation of the host rocks. Dating of monazite and xenotime confirmed the magmatic origin of the corona cores, while LA-ICP-MS dating of allanite established a date of ~ 60 Ma for corona formation and deformation in the Austroalpine basement.

The crystal structure of the mineral decrespignyite-(Y) from the Paratoo copper mine (South Australia) has been obtained by applying δ recycling direct methods to 3D electron diffraction data followed by Rietveld refinements of synchrotron powder diffraction data. Its structure mainly shows a metal layer sequence of polyhedra interconnecting hexanuclear (octahedral) oxo-hydroxo yttrium clusters along a ternary axis or tilted clusters to hetero-tetranuclear ones hosting Cu, Y and rare earths.