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The water dissolution mechanism in silicate melts under high pressures is not well understood. Here we present the first direct structure investigation of a water-saturated albite melt to monitor the interactions between water and the network structure of silicate melt at the molecular level. In situ high-energy X-ray diffraction was carried out on the NaAlSi3O8-H2O system at 800 °C and 300 MPa, at the Advanced Photon Source synchrotron facility. The analysis of the X-ray diffraction data was augmented with classical Molecular Dynamics simulations of a hydrous albite melt, incorporating accurate water-based interactions. The results show that metal–oxygen bond breaking at the bridging sites occurs overwhelmingly at the Si site upon reaction with H2O, with subsequent Si–OH bond formation and negligible Al–OH formation. Furthermore, we see no evidence for the dissociation of the Al3+ ion from the network structure upon breaking of the Si–O bond in the hydrous albite melt. The results also indicate that the Na+ ion is an active participant in the modifications of the silicate network structure of the albite melt upon water dissolution at high P–T conditions. We do not find evidence for the Na+ ion dissociating from the network structure upon depolymerization and subsequent formation of NaOH complexes. Instead, our results show that the Na+ ion persists as a structure modifier with a shift away from Na–BO bonding to an increase in the extent of Na-NBO bonding, in parallel with pronounced depolymerization of the network. Our MD simulations show that the Si–O and Al–O bond lengths are expanded by about 6% in the hydrous albite melt compared to those of the dry melt at high P–T conditions. The changes in the network silicate structure of a hydrous albite melt at high pressure and temperature, as revealed in this study, must be considered in the advancement of water dissolution models of hydrous granitic (or alkali aluminosilicate) melts. [ABSTRACT FROM AUTHOR]

Critical aspects of the crystallization dynamics of H2O-saturated melts of a typical granitic composition as well as granitic melts enriched in lithium (8800 ppm) were investigated in real-time experiments using the hydrothermal diamond anvil cell at 480-700 °C and 220-960 MPa. Complete crystallization of the charges was achieved within 5-118 h with average crystal growth rates ranging from 3 to 41 cm/year for quartz and from 18 to 58 cm/year for alkali feldspars, demonstrating that crystals formed from a silicate melt in the presence of a coexisting aqueous phase crystallize rapidly. The combination of substantial nucleation delays, low nucleation densities, and rapid growth rates for quartz and alkali feldspars led to the formation of euhedral megacrysts of these minerals in the vicinity of clusters comprised of much smaller muscovite or α-spodumene crystals. Subsolidus replacement processes initiated during crystal-fluid interactions after the silicate melt was consumed were directly observed in the experiments. The experimental results underscore the important role of water as a medium for the transport of essential elements such as Si, Al, Na, and K from the silicate melt to the newly formed crystals, and provide important insights into the crystallization of miarolitic pegmatites. [ABSTRACT FROM AUTHOR]

Studies of microbiota reveal inter-relationships between the microbiomes of the gut and lungs. This relationship may influence the progression of lung disease, particularly in patients with cystic fibrosis (CF), who often experience extraoesophageal reflux (EOR). Despite identifying this relationship, it is not well characterised. Our hypothesis is that the gastric and lung microbiomes in CF are related, with the potential for aerodigestive pathophysiology. We evaluated gastric and sputum bacterial communities by culture and 16S rRNA gene sequencing in 13 CF patients. Impacts of varying levels of bile acids, pepsin and pH on patient isolates of Pseudomonas aeruginosa (Pa) were evaluated. Clonally related strains of Pa and NTM were identified in gastric and sputum samples from patients with symptoms of EOR. Bacterial diversity was more pronounced in sputa compared to gastric juice. Gastric and lung bile and pepsin levels were associated with Pa biofilm formation. Analysis of the aerodigestive microbiomes of CF patients with negative sputa indicates that the gut can be a reservoir of Pa and NTM. This combined with the CF patient's symptoms of reflux and potential aspiration, highlights the possibility of communication between microorganisms of the gut and the lungs. This phenomenon merits further research. [ABSTRACT FROM AUTHOR]