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The solubility of quartz has been measured in a wide range of salt solutions at 800°C and 0.5 GPa, and in NaCl, CaCl 2 and CsCl solutions and H 2 O-CO 2 fluids at six additional P-T conditions ranging from 400°C at 0.1 GPa to 800°C at 0.9 GPa. The experiments cover a wide range of compositions along each binary. At P-T conditions where the density of pure water is low (0.43 g cm )3 ), addition of most salts produces an enhancement of quartz solubility at low to moderate salt concentrations (salt-in effect), although quartz solubility falls with further decrease in X H 2 O. At higher fluid densities (0.7 g cm )3 and greater), the salt-in effect is generally absent, although this depends on both the cation present and the actual P-T conditions. The salt-in effect is most readily produced by chloride salts of large monovalent cations, while CaCl 2 only produced a salt-in effect at the most extreme conditions of high-T and low-P investigated (800°C at 0.2 GPa). Under most crustal conditions, the addition of common salts to aqueous fluids results in a lowering of quartz solubility relative to that in pure water (salt-out effect). Comparing quartz solubility in different fluids by calculating X H 2 O on the basis that all salts are fully associated under all conditions yields higher quartz solubility in solutions of monovalent salts than in solutions of divalent salts, absolute values are also influenced by cation radius.Quartz solubility measurements have been fitted to a Setchenow-type equation, modified to take account of the separate effects of both the lowering of X H 2 O and the specific effects of different salts, which are treated as arising through distinct patterns of non-ideal behaviour, rather than the explicit formation of additional silica complexes with salt components. Quartz solubility in H 2 O-CO 2 fluids can be treated as ideal, if the solvation number of aqueous silica is taken as 3.5. For this system the solubility (molality) of quartz in the binary fluid, S is related to its solubility in pure water at the same P-T conditions, S o , by: log S ¼ log S o þ 3:5 log X H2O :Quartz solubility in binary salt systems (H 2 O-RCl n ) can be fitted to the relationship:where salt concentration mRCl n is expressed as molality and the exponent b has a value of 1 except under conditions where salting-in is observed at low salt concentrations, in which case it is <1. Under most crustal conditions, the solubility of quartz in NaCl solutions is given to a good approximation by:We propose that quartz solubility in multicomponent fluids can be estimated from an extended expression, calculating X H 2 O based on the total fluid composition (including dissolved gasses), and adding terms for each major salt present. Our experimental results on H 2 O-NaCl-CO 2 fluids are satisfactorily predicted on this basis. An important implication of the results presented here is that there are circumstances where the migration of a fluid from one quartz-bearing host into another, if it is accompanied by re-equilibration through catio...

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The metastable superheated solutions are liquids in transitory thermodynamic equilibrium inside the stability domain of their vapor (whatever the temperature is). Some natural contexts should allow the superheating of natural aqueous solutions, like the soil capillarity (low T superheating), certain continental and submarine geysers (high T superheating), or even the water state in very arid environments like the Mars subsurface (low T) or the deep crustal rocks (high T). The present paper reports experimental measurements on the superheating range of aqueous solutions contained in quartz as fluid inclusions (Synthetic Fluid Inclusion Technique, SFIT) and brought to superheating state by isochoric cooling. About 40 samples were synthetized at 0.75 GPa and 530-700 °C with internally-heated autoclaves. Nine hundred and sixty-seven inclusions were studied by micro-thermometry, including measuring the temperatures of homogenization (Th: L + V → L) and vapor bubbles nucleation (Tn: L → L + V). The Th-Tn difference corresponds to the intensity of superheating that the trapped liquid can undergo and can be translated into liquid pressure (existing just before nucleation occurs at Tn) by an equation of state. Pure water (840-935 kg m −3 ), dilute NaOH solutions (0.1 and 0.5 mol kg −1 ), NaCl, CaCl 2 and CsCl solutions (1 and 5 mol kg −1 ) demonstrated a surprising ability to undergo tensile stress. The highest tension ever recorded to the best of our knowledge (−146 MPa, 100 °C) is attained in a 5 m CaCl 2 inclusion trapped in quartz matrix, while CsCl solutions qualitatively show still better superheating efficiency. These observations are discussed with regards to the quality of the inner surface of inclusion surfaces (high P-T synthesis conditions) and to the intrinsic cohesion of liquids (thermodynamic and kinetic spinodal). This study demonstrates that natural solutions can reach high levels of superheating, that are accompanied by strong changes of their physicochemical properties.

Water is famous for its anomalies, most of which become dramatic in the supercooled region, where the liquid is metastable with respect to the solid. Another metastable region has been hitherto less studied: the region where the pressure is negative. Here we review the work on the liquid in the stretched state. Characterization of the properties of the metastable liquid before it breaks by nucleation of a vapour bubble (cavitation) is a challenging task. The recent measurement of the equation of state of the liquid at room temperature down to − 26 MPa opens the way to more detailed information on water at low density. The threshold for cavitation in stretched water has also been studied by several methods. A puzzling discrepancy between experiments and theory remains unexplained. To evaluate how specific this behaviour is to water, we discuss the cavitation data on other liquids. We conclude with a description of the ongoing work in our groups.