We experimentally explored direct entrapment of breyite (CaSiO₃) by diamond at upper-mantle conditions in a model subducted sediment rather than formation by retrogression of CaSiO₃ perovskite, implying a deeper origin. Anhydrous low-T melting of CaCO₃+SiO₂ precludes breyite formation. Under hydrous conditions, reduction of melt results in graphite with breyite. Thus, breyite inclusions in natural diamond may form from aragonite + coesite or carbonate melt at 6–8 GPa via reduction with water.

The paper presents experimental results on the growth of diamonds in Fe–Ni melt together with silicate minerals at high P–T. The morphology of the grown diamonds was studied, as well as the chemical composition of the synthetic silicates. This work builds on our preliminary experimental work presented in Zhimulev et al. (2012), which was an experimental evidence to confirm the hypothesis of crystallization of diamonds from metallic liquids explained in a pioneer paper by Smith et al. (2016).

Our research found that the cookeite crystallized within a closed space (e.g., crystal-rich inclusion, CI, in pegmatites) at relatively high P–T conditions might bear distinct and high-purity Raman signals. As a result, this type of cookeite is unusual and provides an indicator of cookeite crystallized in the closed spaces of a primary inclusion (e.g., CI), beneficial for recognizing the primary nature of the CIs in pegmatites and understanding the formation mechanisms of CIs and pegmatites.

There have been many different ages found for ophiolite. We have researched these ages through fieldwork and microscopy to identify three types of dunite. These are useful ways to research the origin of ophiolitic magma. The Purang ophiolite, which crops out over an area of about 650 km² in the western Yarlung–Zangbo suture zone, chiefly consists of mantle peridotite, pyroxenite and gabbro. It is a useful ultra-massif for showing the multistage nature of ophiolite.

A mineral from Ettringer Bellerberg (Eifel, Germany) proved to be a polytype of the important ceramic-phase mullite termed mullite-2c, with – similar to sillimanite – doubling of the c lattice parameter due to strong (Si,Al) order in tetrahedral diclusters and – similar to mullite – presence of oxygen vacancies and tetrahedral triclusters due to Al / Si > 1 in diclusters. Crystals were characterised using single-crystal XRD, electron microprobe analysis (EMPA) and spindle-stage optical methods.

This paper describes the characterization of a new mineral from the Oumlil mine in the Bou Azzer cobalt mining district in Morocco. This mining district is one of the world's largest producers of the important element cobalt. This study on the new mineral halilsarpite provides useful information on the results of chemical weathering processes on the primary arsenide minerals at the mine.

It is shown here that the H₂O content of hydrous minerals can be determined from their mean refractive indices with high accuracy. This is especially important when only small single crystals are available. Such small crystals are generally not suitable for thermal analyses or for other reliable methods of measuring the amount of H₂O. The results are compared with the observed H₂O content evaluating 157 zeolite-type compounds and 770 non-zeolitic hydrous compounds, showing good agreement.

The Neolithic polished stone industry of Chiomonte was studied with a multi-analytical approach, with the aim of providing information about the raw material origins and supply sources. Most tools are made of greenstones. Specific mineral and chemical markers were found, pointing to an origin in the Monviso area. The presence on roughouts and broken tools with raw surfaces ascribable to pebbles or cobbles suggests that these rocks had been picked up from glacial or alluvial secondary sources.

Type material for heliophyllite, preserved in the Swedish Museum of Natural History in Stockholm, was re-investigated through a combined EPMA (electron probe X-ray microanalysis), Raman, and X-ray powder diffraction (XRPD) and single-crystal study. EPMA chemical data, together with Raman and single-crystal structural studies, point to heliophyllite being identical to ecdemite. XRPD synchrotron data highlight the presence of a minor quantity of finely admixed finnemanite in the analyzed material.

Feldspars are the most abundant minerals in the Earth's crust. Their structural behaviour is complicated because order/disorder reactions, phase transitions, and unmixing processes interact. Liu et al. (2018) claim that the water content in the nominally dry feldspars has a profound influence on the transformation behaviour. Their arguments, however, are not sound. We point to a number of errors and omissions.

Laurentthomasite is a new mineral from Madagascar showing a very strong dichroism going from deep blue to yellow-green colours. The physical and chemical characteristics of this gem quality mineral bring it to the attention of the jewel industry as well as collectors of cut stones.

Quartz is a very common form of almost pure silica. It can contain a small concentration of hydrogen-bearing defects whose nature is still debated. Here, we use a theoretical approach to unravel the atomic-scale geometry of these defects. Our findings help explain some important quartz properties.

Molybdates are of a great interest due to their ionic conductivity, negative thermal expansion, and immobilization of radionuclides. The new mineral tancaite-(Ce), FeCe(MoO₄)₃•3H₂O, shows a new structure type never observed in natural and synthetic molybdates. Its cubic average structure may be described as a derivative of the perovskite structure, in which Fe-centred octahedra are linked through MoO₄ groups. The ordering of Mo and O atoms results in one or more complex superstructures.

Rhönite in the Cenozoic alkali basalts of the Changle area occurs as a reaction product; the host basalts are generated in an extensional setting of intracontinent and are tectonically located above the old subduction zone. Rare-earth-element patterns of rhönite resemble those of kaersutitic amphibole and kaersutite. Compositions of Changle rhönites covering the two types of metasomatic mantle amphiboles further suggest that rhönite could be seen as the role of petrogenetic indicator mineral.

Partition coefficients are key to petrological modelling yet hard to estimate independently of measurements. Here we model the partitioning of Cr between garnet and clinopyroxene ab initio. Incorporation of Cr into crystal structures causes strain, and its energetic toll defines whether Cr favours one mineral or another. Comparing to Cr content in metamorphic rocks shows how mineral composition and structure set equilibrium partition coefficients and how kinetics hampers equilibrium.

Zoisite eclogites from the Sanddal area, North-East Greenland, contain numerous textures, such as cusps and neoblasts, which are interpreted as melt-related textures. Mineral chemistry and thermodynamic modeling demonstrate that they were partially melted through the breakdown of hydrous minerals, phengite, paragonite and zoisite. Pressure–temperature phase diagrams show that the eclogites reached a maximum depth of ∼70 km and were partially melted near that depth and during exhumation.

Feldspars constitute about 60 % of the earth's crust. Na-feldspar, Na[AlSi₃O₈], is central to this mineral group. Its structural response to changing conditions of temperature and pressure is complicated. In particular, this applies to the distribution of Al and Si on the atomic sites of its crystal structure. We clarify how this distribution varies in thermodynamic equilibrium with external conditions and provide procedures that allow easy determination of the atomic distribution.