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.

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.

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.

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.

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. 

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.

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.

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.