Kamafugites are rare ultrabasic/basic K₂O-rich rocks. High-pressure–high-temperature experiments on four samples from the known type localities (Italy, Brazil, Uganda) constrained their melting assemblage, unlike a classical peridotite. Clinopyroxene and phlogopite are the first near-liquidus phases. Olivine appears in two runs. The different abundances of the main phases and the variable contribution of apatite, oxides and titanite explain the variegated kamafugite geochemical features.

We used U–Pb dating and Pb–Sr–O–H isotopes of hydrothermal epidote to characterize fluid circulation in the Aar Massif (central Swiss Alps). Our data support the hypothesis that Permian fluids exploited syn-rift extensional faults. In the Miocene during the Alpine orogeny, fluid sources were meteoric, sedimentary, and/or metamorphic water. Likely, Miocene shear zones were exploited for fluid circulation, with implications for the Sr isotope budget of the granitoids.

Karlseifertite is a new member of the dussertite group of the alunite supergroup from Tsumeb, Namibia. It is the first member of the dussertite group to be described based upon valency-imposed double site occupancy in the octahedrally coordinated cation site. It is also the first member of the alunite supergroup containing essential Ge. 

The article provides the standard description of bonacinaite, Sc³⁺(AsO₄)·2H₂O, the first natural scandium arsenate. The new mineral species was found in a few specimens in the dumps of the old Varenche Mine, Valle d'Aosta, Italy, which is therefore the type locality and the only locality in the world. Bonacinaite forms colourless (with faint to distinct violet tints), pseudohexagonal, thick tabular crystals, up to 0.25 mm in size, or as small, faintly violet lath-shaped crystals.

We experimentally investigated the behavior of chrome in high-pressure post-spinel oxide phases. Only minor amounts of Cr can be incorporated into Fe₅O₆. But there is full solid solution between Fe₄O₅ and Fe₂Cr₂O₅ and Mg₂Fe₂O₅ and Mg₂Cr₂O₅, in spite of a phase transition occurring in the middle of the compositional range. Our results provide further constraints on the formation of such oxide phases in extraterrestrial materials and inclusions in natural diamonds.

Technology for producing energy with zero-carbon emissions must be developed in light of the current climate emergency. Using recyclable metal fuels, such as magnesium (Mg), is one practical solution. Metals can therefore be seen as regenerable fuels and new energy vectors since the energy they contain can be transferred and released through metal combustion. To optimize the particle trapping capacity of the investigated system, we successfully characterized magnesium oxide (MgO) crystals. 

Known as black smokers, sulfur-rich hydrothermal vents expel hot metal-rich water (~ 400°C). These extreme environments host micro-organisms capable of living at over 100°C. But to date, we do not know whether these microorganisms influence the formation of hydrothermal vents. The comparative study of minerals along the chimney wall is an essential step in determining whether microorganisms may have colonized and influenced mineral formation in certain parts of the chimney. 

The discovery of the K-dominant tourmaline maruyamaite with microdiamond inclusions suggested its ultrahigh-pressure formation. We analyzed the role of K in the tourmaline structure, with a special focus on its stability. High pressure is necessary to squeeze the large cation K⁺ in the stiff framework of tourmaline, although K is the underdog component if Na⁺ is present in the mineralizing fluid. K-tourmaline is stable at high pressure, overcoming the stereotype of a mere crustal component.

In this study, we analyze a peculiar eclogite from the Western Alps, which not only recorded a classical subduction-to-exhumation path but revealed evidence of Ca-rich fluid–rock interaction. Chemical composition and modeling show that the rock experienced peak metamorphic conditions followed by Ca-rich pulsed fluid influx occurring consistently under high-pressure conditions. This research enhances our understanding of fluid–rock interactions in subduction settings.

This work deals with a challenging case of a commercial clay from Gomsiqe–Puka (Albania) contaminated by mineral fibres. Detection and quantification of asbestos in this material push the boundaries of current experimental methods. Using TEM, micro-Raman spectroscopy, and EPMA, we identified the presence of asbestos tremolite, along with a rare fibrous variety of diopside. The impact of milling on the detection and quantification of mineral fibres was also evaluated.

Lascar volcano, located in northern Chile, is among the most active volcanoes of the Andes. Its activity culminated in the last major explosive eruption in April 1993. We carried out experiments at high temperatures (up to 1050 °C) and pressures (up to 5000 bar) in the lab, and we used a wide variety of geochemical methods to provide comprehensive constraints on the depth and temperature of the magma chamber beneath Lascar volcano.

Dauphiné twin (DT) domains in a deformed quartz were visualized for the first time by using orientation-optimized electron channelling contrast imaging under Bragg conditions of the rhombohedral planes. The different contrast of a pair of DT domains in the backscattered electron images originates not from a misorientation between the two domains but from different diffraction intensities between positive and negative rhombohedral planes in quartz.

Ardennite is a rare Mn-rich aluminosilicate that was originally described in Salmchâteau, Belgium. In the last few years, new samples of ardennites have been found at several localities close to Salmchâteau. These samples were analysed by electron microprobe, single-crystal X-ray diffraction, and infrared spectroscopy. The results given in this paper allow us to identify the main substitution mechanisms that occur in Belgian ardennites and to discuss the nomenclature of the ardennite group.

This article reviews the crystal chemistry of chlorite, biotite, and white mica in metamorphosed sediments. These minerals have complex compositions because many atom exchanges may take place in their structure. Such exchanges include easily measured cations but also structurally bound H₂O, notoriously hard to measure; iron oxidation; and vacancies. Consequently, formula units are often calculated from incomplete measurements and some exchanges may appear solely due to normalization issues.

A new sulfosalt mineral species, lazerckerite, Ag_3.7Pb_4.6(Sb_7.9Bi_3.8)_Σ11.7S₂₄, has been found, identified, structurally solved, and approved by the IMA. The mineral belongs to the Sb–Bi mixed members of the andorite branch of the lillianite homologous series. The description and characterization of the mineral are presented, and the ways of distinguishing the mineral from other similar members of the group on the basis of chemical results are explained.

We studied the exchange of chemical elements by diffusion between magmas of tephritic and phonolitic composition from the Canary Islands, performing experiments at high pressure and high temperature with different amounts of added water. Our results characterize the way water and temperature affect the diffusion process, and we also find unexpectedly high mobility of aluminium, which may be related to its variable chemical bonding in highly alkaline melts. 

The As₄S₆ molecule was missing in the reported structures of crystalline As chalcogenides. Here we report the first occurrence of the As₄S₆ molecule together with the other known As₄S_n (n = 3, 4, 5) molecules randomly replacing each other in the crystalline structure of a new monoclinic product obtained by the light-induced alteration of the mineral alacranite, As₈S₉.

Rotherkopfite is the first member of the neptunite group that does not contain lithium in its chemical formula. It was found at Rother Kopf, Eifel volcanic fields, Germany, where in occurs in cavities in a quartz–sanidine fragment embedded in a volcanic rock. Rotherkopfite occurs as dark brownish-red crystals, up to about 0.2 mm across. The intriguing crystal structure is based on two interwoven three-dimensional frameworks.

Mechanical interaction between quartz inclusions in garnet creates residual pressure in the inclusion used to calculate the pressure and temperature where the two minerals formed. We crystallised quartz and garnet at high pressure and temperature and then adjusted the experimental pressure to observe the interaction between the quartz inclusions and garnet host. The quartz and garnet adjust to the new experimental pressures, reset inclusion pressures, and no longer match entrapment conditions.

To explore the influence of the redox state of the environment on the serpentinization reaction, we have developed an original experimental setup. Reducing conditions, leading to the formation of serpentine and magnetite, and oxidizing conditions, leading to the formation of serpentine and hematite, are discussed in terms of analogues of low- and high-permeability hydrothermal systems, respectively. The influence of the redox on brucite stability and hydrogen production is also established.