Thermochemistry of carbonate-pyroxene equilibria

Article Abstract:

The enthalpy of a well-defined final state of drop-solution of carbonates into molten lead borate reveals the presence of dissolved oxide and evolved CO2, and suggests that oxide melt calorimetry is useful to carbonates. The comparison of the enthalpies from calorimetric measurements with those from phase equilibrium studies can be used to test the calorimetric method for carbonates. Under a flowing gas atmosphere, the enthalpies of many carbonate-quartz reactions are obtained from drop solution calorimetric measurements for dolomite, calcite, enstatite, magnesite, wollastonite, diopside and quartz in lead borate solvent at 977 Kelvin. High temperature oxide melt calorimetry is useful for carbonate thermochemistry.

Analysis, Carbonates

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Cooling rate variation in natural volcanic glasses from Tenerife, Canary Islands

Article Abstract:

Relaxation geospeedometry facilitates the determination of cooling history of phonolite glasses from Tenerife, Canary Islands. Modeling of the enthalpy relaxation, using heat capacity measurements by differential scanning calorimetry, indicates a range of quench rates covering five orders of magnitude. Apart from cooling due to heat loss by radiation from the surface, these glasses have suffered slow cooling by a natural annealing process and rapid cooling induced by volatile degassing. The effects of the overall heat budget and other factors on the cooling rate are discussed.

Rocks, Igneous, Igneous rocks, Earth temperature, Earth's temperature

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The reaction MgCr2O4 + SiO2 = Cr2O3 + MgSiO3 and the free energy of formation of magnesiochromite (MgCr2O4)

Article Abstract:

Thermodynamic data for magnesiochromite were obtained by analyzing the reaction MgCr2O4 + SiO2 = Cr2O3 + MgSiO3 in the pressure-time domain. The results were then compared with other published values of thermodynamic properties for orthoenstatite, beta-quartz and eskolaite to derive the entropy and enthalpy of formation of MgCr2O4. The results suggested that the available calorimetrically obtained figure for the entropy of MgCr2O4 was approximately 16 joules per kelvin per mole below the real value.

Thermodynamics, Chromite

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