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Djerfisherite is an important carrier of potassium in highly reduced enstatite chondrites, where it occurs in sub-round metal-sulfide nodules. These nodules were once free-floating objects in the protoplanetary nebula. Here, we analyze existing and new data to derive an equation of state (EOS) for djerfisherites of [K.sub.6][(Cu,Fe,Ni).sup.B][(Fe,Ni,Cu).sup.C.sub.24][S.sub.26]Cl structural formula. We use this EOS to calculate the thermal stability of djerfisherite coexisting in equilibrium with a cooling vapor of solar composition enriched in a dust analogous to anhydrous, chondritic interplanetary dust (C-IDP). We find that condensed mineral assemblages closely match those found in enstatite chondrites, with djerfisherite condensing above 1,000 K in C-IDP dust-enriched systems. Results may have implications for the volatile budgets of terrestrial planets and the incorporation of K into early formed, highly reduced, planetary cores. Previous work links enstatite chondrites to the planet Mercury, where the surface has a terrestrial K/Th ratio, high S/Si ratio, and very low FeO content. Mercury's accretion history may yield insights into Earth's. Keywords Nebula * Condensation * Potassium * Chondrite * Mercury * Core heating * Thermodynamics, Introduction Djerfisherite is an accessory mineral in ultra-alkalic terrestrial magmas (e.g., Henderson et al. 1999; Zaccarini et al. 2007) and kimberlites (Clarke et al. 1994; Sharygin et al. 2007), but [...]

Significant quantities of silver can be accommodated in galena as a coupled substitution with Ag + Sb and/or Ag + Bi for 2 Pb atoms. The limitations of this solubility are quantified experimentally for the cubic (Fm[bar.3]m) [alpha]-galena phase. Above 441.7 [degrees]C, the [alpha]-galena phase has complete solid solution across the [Pb.sub.2][S.sub.2]-AgSb[S.sub.2]-AgBi[S.sub.2] (galena-miargyrite-matildite) ternary. Dry sinter experiments at 400, 375, and 350 [degrees]C extend the known miscibility gap on the [Pb.sub.2][S.sub.2]-AgSb[S.sub.2] binary into ternary compositions. Phase equilibrium and miscibility gap data and self-consistent thermodynamic data for other high-temperature phases in this system combined with data for other sulfides and sulfosalts are used to constrain an asymmetric regular solution model for the [alpha]-galena phase ([Pb.sub.2],AgSb,AgBi) [S.sub.2]. Phase relations in this system suggest that simple retrograde re-equilibration during cooling can produce phase assemblages and textures commonly observed in Ag-bearing ore deposits. Bulk metal ratios of deposits in conjunction with the application of this thermodynamic model may be used to understand district Ag-distribution or as an exploration tool. Keywords: Experimental petrology, Ag in galena, phase equilibria, thermodynamics, silver deposits

Tetrahedrite fahlores from the Galena Mine of the Coeur d'Alene Mining District (Wallace, Idaho) have been found to be enriched in Ag by the Ag-Cu exchange reaction: 1/10 [Cu.sub.10][(Zn,Fe).sub.2][Sb.sub.4] [S.sub.13] + AgSb[S.sub.2] + PbS = CuPbSb[S.sub.3] + 1/10 A[g.sub.10] [(Zn,Fe).sub.2][Sb.sub.4] [S.sub.13] Cu-fahlore in galena galena boumonite Ag-fahlore which occurred during cooling following fahlore mineralization. This solid-state reaction produced a distinct population of high-Ag fahlores found in galena-rich samples, quantitatively removed Ag (in an AgSb[S.sub.2] component) from galena, and accounts for all of the bournonite mineralization. This reaction has produced the most argentian fahlore yet found [molar Ag/(Ag + Cu) = 0.443] in the district, and forms a secondary overprint on any primary fahlore zoning that may have existed. The results obtained here indicate that the galena and fahlore-siderite stages of mineralization were virtually synchronous, as this reaction has produced the same result despite the opposite relative age relationships of these mineralization stages exhibited in two of the mines studied. Multiple lines of evidence suggest a temperature between 320 and 350 [degrees]C for this 'stage.' Based on the Ag/(Ag + Cu) of fahlores and Fe-Zn partitioning between fahlore and sphalerite, we estimate that fahlore compositions were frozen in by about 235 [degrees]C, roughly 40 [degrees]C above corresponding temperatures obtained for the Gold Hunter vein of the Lucky Friday Mine. This result and the absence of readily detectable diaphorite (~[Pb.sub.2][Ag.sub.3][Sb.sub.3][S.sub.8]) in the Galena Mine sample containing the highest Ag fahlore indicate a faster cooling rate for the terrane in the vicinity of the Galena Mine.

A study indicates that the source region of martian shergottites is greatly less oxidized and less Fe-enriched than previously reported values and is depleted even more in other major elements. The discrepancies in the shergottite source region values suggest that the source region is due to an extensive batch-melting of a more fertile mantle. The constraint on the shergottite source region's depth estimate also suggests the formation from a body bigger than an asteroid.

A regular solution-type thermodynamic model, for twelve component silicate liquids, can be used for natural hydrous and anhydrous magmatic compositions. The temperature is in the range of 900 to 1700 degrees centigrade and pressures up to four GPa. Simulation of igneous processes, such as fractional crystallization and degassing of volatiles, can be done using the model, which is used as a software package.

A new thermodynamic model, for studying Gibbs free energy of igneous pyroxenes, is based on general formulation and is dependent on the calibration of a quadrilateral subsystem. The model is made using experimental data of compositions of co-existing pyroxenes and silicate melt. The general formula of pyroxenes, under study, is given and the thermodynamics of multicomponent pyroxenes is discussed.

A thermodynamic model is developed for pyroxenes in the chemical (mineralogical) system CaMgSi2O6 (diopside, Di, 1) - CaTiAlSiO6 (grossmanite, Gr, 2) - CaMg1/2 Ti1/2AlSiO6 (alumino - buffonite, AlBf, 3) - CaAl2SiO6 (Calcium Aluminum Tschermaks, CATS, 4), aka fassaites. It is formulated for the assumptions of molecular mixing between AlBf and Di, Gr and CATS components, and that the reduction in configurational entropy resulting from short - range Al - Si ordering on tetrahedral sites may be described using, as a proxy, a long-range, convergent ordering parameter for ordering of Al and Si between A and B tetrahedral sites on the AlBf - free tetrahedral sublattice. Nine out of sixteen independent thermodynamic parameters are calibrated to be consistent with calorimetric measurements of Benisek and others (2007), spectroscopic and statistical mechanical constraints on tetrahedral Al - Si ordering in pyroxenes on the Di - CATS binary (Cohen, 1986; Vinograd, 2001; Warren and others, 2001), and phase equilibrium constraints on Di - AlBf miscibility gaps in the Di - AlBf - CATS ternary subsystem (Yang 1975, 1976). The remaining seven independent parameters (for Gr - bearing fassaites) are constrained to be consistent with the distribution of fassaite compositions in calcium - aluminum - rich inclusions in carbonaceous chondrites (CAIs), experimental determinations of fassaite single - phase regions produced at the extremely low oxygen fugacities prevailing during their primary condensation/crystallization (for example, Beckett, ms, 1986), and the assumption that secondary fassaites in Wark - Lovering rims enclosing CAIs were in local equilibrium with the outer surface layers of the earlier (canonical) AlBf - rich fassaites at their layer contacts at temperatures of around 1473 K (Wark and Lovering, 1982; Meeker and others, 1983; Murrell and Burnett, 1987; Ruzicka, 1997; Dyl and others, 2011). In this model there is a miscibility gap between Di-rich and AlBf-rich fassaites on the Di - AlBf join which displays only very limited extension into the fassaite tetrahedron. On the Di - AlBf - CATS face of this tetrahedron there is a second miscibility gap (upper buffonite gap, UBG) with 0.08 < X4fas < 0.22 and 0.06 < X4fas < 0.25 at 1505 and 1473 K. This gap is modestly ellipsoidal with its long axis roughly radial to AlBf and it is roughly symmetrically disposed between Di and AlBf at 1505 K. At 1473 K this gap extends to the AlBf - CATS binary, intersecting it at very low and intermediate X4fas, with most of its CATS - rich binode being metastable with respect to assemblages composed of the minerals melilite, spinel, anorthite, perovskite and CATS - poor fassaite. A third miscibility gap extends from the CATS-rich portion of the AlBf - CATS binary, and occupies most of the CATS - rich portion of this ternary at 1505 and 1473 K. It is metastable with respect to assemblages composed of melilite, spinel, anorthite, perovskite and hibonite, and, has a CATS - rich binode that is virtually coincident with the Di-CATS binary at high CATS contents, in accordance with compositions of metastable, virtually AlBf-free CATS-rich fassaites (kushiroites) found in hibonite ≈ grossite + fassaite spherules in CAIs (for example, Krot and others, 1999). Within the fassaite tetrahedron at 1473 K the UBG is rapidly destabilized with addition of the Gr component, diminishing in dimension and collapsing to a critical endpoint at X2fas < 0.06. With further increase in Ti(Al)-1 exchange potential, the third miscibility gap in Di - AlBf - CATS fassaites (where it is metastable) becomes less extensive, and, it separates into an interior gap and one emanating from the Gr - AlBf - CATS ternary at a Ti(Al)-1 exchange potential corresponding to a reference Gr - CATS fassaite with X2fas (=Xref2) ≈ 0.22. Both of these gaps continue to decrease in size with further increases in Ti(Al)-1 exchange potential, with the gap emanating from the Gr - AlBf - CATS ternary terminating there in a critical point at X2 ref ≈ 0.30. With further increase in Ti(Al)-1 exchange potential the more Di-rich gap continues to move toward the Di - Gr - CATS ternary until X2 ref ≈ 0.50. At higher Ti(Al)-1 exchange potentials there is complete miscibility in quaternary fassaites, except in the immediate vicinity of the Di - AlBf binary, and, at very high Ti(Al)-1 exchange potentials, in fassaites near the Di - Gr binary. Evaluating the Ti(Al)-1 exchange potentials at which the extensive gap that is metastable in the diopside - alumino - buffonite - CATS ternary subsystem becomes stable in the quaternary system at given temperatures awaits development of a comprehensive database for CAI fassaites and their associated minerals, particularly the solid solutions melilite and hibonite (for example, Waldbaum, 1973; Waldbaum and Woodhead, 1975; Doyle and others, 2014). The model for fassaite thermochemistry is used to develop a Ti3+ - Ti4+ fassaite oxygen cosmobarometer based on experimental constraints (for example, Beckett, ms, 1986). Values of oxygen fugacity calculated with this cosmobarometer for fassaites and melilites, judged by Grossman and others (2008) to be coeval in refractory CAIs from the Allende carbonaceous chondrite, are more than three orders of magnitude below that of a gas of solar composition. [ABSTRACT FROM AUTHOR]

Research was conducted to develop numerical models for the compaction of olivine cumulates using simultaneous grain boundary diffusion (GBD) creep and power law creep. The model incorporates compaction, thermal conduction, porous medium flow, advection of heat and crystallization. The model suggests that the crystals will be lithified into a mass with strength that is within meters of the depositional surface GBD driven compaction even if deposited by sedimentation.

A thermodynamic model for the mixing properties of MgAl2O4-Al8/3O4 spinels is formulated, calibrated, and used to develop a closed-form polynomial for the excess Gibbs energy of mixing. The model is formulated on the assumptions that Mg, Al and vacancies exhibit long-range-ordering (LRO) between tetrahedral and octahedral sites, and that the vibrational Gibbs energy may be described by a Taylor expansion of second degree in the composition variable X ≡ 3/2 (2AlOCT + XAlOCT + XAlTET - 2) = (3XVacTET + 6XVacOCT) and in LRO variables S1 ≡ XAlOCT - 1/2 XAlOCT and S2 = (3XVacTET + 6XVacOCT. Calibration of the parameters produces a model that, in addition to being consistent with spectroscopic constraints on Mg-Al ordering in MgAl2O4-rich spinels, successfully reproduces the brackets on the compositions of MgAl2O4-Al8/3O4 spinels coexisting with corundum over the temperature range 1400 to 2200 K, employing only a few mixing parameters and making physically plausible predictions, such as random distribution of vacancies and Al between octahedral and tetrahedral sites in the metastable, cubic γ-Al8/3O4 endmember. The resulting activity-composition relations for MgAl2O4-Al8/3O4 spinels are extremely simple and show minimal (Al8/3O4) to negligible (MgAl2O4) temperature dependence. [ABSTRACT FROM AUTHOR]