The high-pressure stability of zoisite and phase relationships of zoisite-bearing assemblages

Article Abstract:

The pressure and temperature at which zoisite breaks down is determined experimentally. The high-pressure thermal properties of zoisite and lawsonite are also derived from their bulk moduli and thermal expansions. Results of the study show that zoisite is stable in waterless reactions between 5.0 GPa at 700 degrees C and at 6.6 GPa at 950 degrees C. Zoisite can be used as geohygrometers because it can occur at water-saturated conditions, water-undersaturated but fluid-absent conditions and water undersaturated but mixed-fluid conditions.

Phase transformations (Statistical physics), Phase transitions (Physics), Minerals (Geology), Rocks, Rock-forming minerals

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Bearthite, Ca2Al(PO4)2OH: stability, thermodynamic properties and phase relations

Article Abstract:

A stoichiometric mixture of gamma-Al2O3 and CaHPO4.2H2O is used to prepare phosphate bearthite Ca2Al(PO4)2OH. The mixture is maintained at pressures between 4 to 24.5 kbar water pressure and temperatures of 485 to 800 degrees centigrade. The compound is stable at both high water pressures and very low pressures. The thermodynamic parameters for bearthite are estimated for dehydration reactions. The phase relations involving the phosphates bearthite, trolleite, berlinite, augelite and hydroxyapatite are investigated.

Thermodynamics, Analytic geochemistry, Phosphate minerals

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Phase diagram methods for graphite rocks and application to the system C-O-H-FeO-TiO2-SiO2

Article Abstract:

The amount of hydrogen or oxygen released or consumed during mineral reactions determines the composition of C-O-H fluid in graphite rocks. The mass balance constraints acting during the fluid-rock interaction are explained by the compositional degree of freedom. The calculation of the C-O-H-FeO-TiO2-SiO2 system petrogenetic grid confirms the pressure-temperature stability field of this assemblage.

Usage, Graphite, Phase diagrams, Degree of freedom

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