The synthetic anhydrous analogue of the mineral leucite has the chemical formula KAlSi2O6, it has a silicate framework crystal structure with the same topology as the zeolite analcime. In this crystal structure Al partially replaces Si in the framework, a K extraframework cation is incorporated to balance the charges. Synthetic analogues of leucite are known with the general formulae ACX 2O6 and A 2 BX 5O12, where A is a monovalent cation, B is a divalent cation, C is a trivalent cation and X is Si or Ge. The crystal structures of these analogues have the same topology but otherwise show differences in crystal structure symmetry and framework cation ordering. This paper reviews the work done on leucite analogue crystal structures over the years and looks forward to work that could be done on these fascinating materials in the future.

The importance of protein crystals for structural studies of biological macromolecules, peculiarities of protein crystals, and their growth under terrestrial and microgravity conditions are considered. The reasons for the better quality of protein crystals grown in space are discussed. The history of protein crystallization experiments under microgravity conditions from the very beginning to the present is briefly reviewed. The contribution of space experiments to the theory of the protein crystallization, the development of new crystallization methods and the design of new crystallization devices is highlighted. The revelation of structure–function relations for some proteins based on their 3D structures solved using crystals grown under microgravity conditions within the framework of the JAXA/PCG project is presented and arguments in favour of space experiments are given.

α-FeOOH exhibits high thermodynamic stability and is the most abundant iron hydroxide in soils and sediments, commonly found as a weathering product in various rocks. Under high pressure, it undergoes a phase transition to the high-pressure phase ϵ-FeOOH. This review discusses the structural, thermal, physical, and spectroscopic properties of α-FeOOH and ϵ-FeOOH. Through a combination of experimental observations and theoretical models, it has been demonstrated that ϵ-FeOOH can form stable solid solutions with δ-AlOOH and MgSiO4H2, thereby extending the stability range of these phases into the lower mantle. The key effects of phase transitions of α-FeOOH and ϵ-FeOOH, including hydrogen bond symmetrization and spin state changes, directly influence the physical properties of these minerals, such as bulk modulus, electrical conductivity, and elasticity. The ultrahigh-pressure phase Py-FeOOHX may decompose in rising mantle plumes, contributing sporadic oxygen sources for the Great Oxidation Event. The Great Oxidation Event, lasting from approximately 2.4 to 2.06 billion years ago, may have been triggered by a prolonged period of instability. Whether other hydrous minerals exhibit similar behaviours, potentially leading to an underestimation of sporadic deep sources, remains an open question for future research.