Recent  

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.

The paper describes the characterisation of fluor-rewitzerite, a new mineral species belonging to the paulkerrite group. The crystal structure of fluor-rewitzerite has been refined using microfocus synchrotron diffraction data, which allowed 25 of the possible 30 H atoms to be located, thus establishing key features of the H bonding. Crystallochemical trends are reviewed for seven recently characterised monoclinic paulkerrite-group minerals.

Zvěstovite-(Fe) is a new, Ag-rich, member of the tetrahedrite group, the most widespread sulfosalts in ore deposits. Its discovery stresses the chemical variability of this mineral group, allowing for a better understanding of the structural plasticity of these compounds, which are able to host a plethora of different elements typical of hydrothermal environments. 

This work presents the results on deformation-enhanced melt segregation and extraction in a phonolitic magma emplaced at shallow depth in the Velay volcanic province (France). We provide evidence of the segregation and subsequent extraction of the residual melt during magma ascent and final emplacement. We highlight that melt segregation started by compaction as a loose packing of microlites emerged and continued with melt filling of a shear band network.

The piston–cylinder apparatus is widely used to investigate rock properties at the conditions of the interior of the Earth, but uncertainty in its calibration of pressure persists, with substantial differences between laboratories. We use a ceramic of magnesium and zinc oxides to measure the conditions experienced by a sample. Routine use of such ceramics provides an archive of experimental conditions, enables interlaboratory comparisons, and resolves long-standing controversies in calibration.

The structure of beryl has been a topic of research for decades but is still not entirely understood. This especially applies to substitutions by Fe ions and the occupation of the channels of beryl by H₂O and alkalis. The growing amount of studies makes it difficult to gain an overview on these topics. Therefore, this article reviews the current consensus and debates found in the literature.