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Abstract This article describes condensation of the elements and use of condensation temperatures to plot and interpret Earth’s apparent volatility trend. Major points covered include the following. (1) Updated 50% condensation temperatures (T₅₀) for all naturally occurring elements, Tc, and Pu are tabulated at 10⁻²to 10⁻⁸bar total pressure for solar composition material. (2) Condensation temperatures are mainly controlled by the Gibbs energy of condensation reactions and also by the Gibbs energy of ideal mixing if elements (compounds) condense in a solution. The additional Gibbs energy change due to non-ideal solution, i.e., activity coefficients ≠1, is a secondary effect. (3) The theoretically correct relationship between condensation temperature and fraction condensed ($$\alpha _{\mathrm{M}}$$ ${\alpha }_M$) is derived from mass balance and chemical thermodynamic considerations. For major elements the condensation temperature is inversely proportional to log (1-$$\alpha _{\mathrm{M}}$$ ${\alpha }_M$). For trace elements dissolving in solid solution the condensation temperature is inversely proportional to log [(1-$$\alpha _{\mathrm{M}}$$ ${\alpha }_M$)/$$\alpha _{\mathrm{M}}$$ ${\alpha }_M$]. (4) The maximum amount of element condensed per K⁻¹, i.e., the maximum in [d$$\alpha _{\mathrm{M}}$$ ${\alpha }_M$/d(1/T)] is at the inflection point in the logistic (sigmoid) curve for an element, which is also at (or close to) the 50% condensation temperature. (5) Plots of normalized elemental abundances versus 50% condensation temperatures (volatility trends) are qualitative indicators of elemental fractionations due to volatility because they do not use the theoretically correct and quantitative relationship between condensation temperature and fraction condensed. (6) Volatility trend plots for average elemental abundances in CM, CO, CV, CR, H, L, LL, EH, EL chondrites show different “trends” for moderately and highly volatile elements, which may be linear, curved, a step function, or plateau. A comparison of three abundance sets for CM and CV chondrites shows trends depend on which elements are plotted, which data sources are used, and which temperature range is considered. (7) Proposed mechanisms for volatile element depletion in carbonaceous chondrites and the Earth are reviewed. (8) Some possible implications of volatile element abundances in the bulk silicate Earth are discussed. 

Abstract From transmission electron microscopy and other laboratory studies of presolar grains, the implicit condensation sequence of carbon-bearing condensates in circumstellar envelopes of carbon stars is (from first to last) TiC-graphite-SiC. We use thermochemical equilibrium condensation calculations and show that the condensation sequence of titanium carbide (TiC), graphite (C(Gr)), and silicon carbide (SiC) depends on metallicity in addition to C/O ratio and total pressure. Calculations were performed for a characteristic carbon star ratio of C/O = 1.2 from 10⁻¹⁰to 10⁻⁴bars total pressure and for uniform metallicity variations ranging from 0.01 to 100 times solar elemental abundances. TiC always condenses at higher temperatures than SiC, and the carbide condensation temperatures increase with both increasing metallicity and increasing total pressure. Graphite, however, can condense in a cooling circumstellar envelope before TiC, between TiC and SiC, or after SiC, depending on the carbon-bearing gas chemistry, which is dependent on metallicity and total pressure. Analytical expressions for the graphite, TiC, and SiC condensation temperatures as functions of metallicity and total pressure are presented. The inferred sequence from laboratory presolar grain studies, TiC-graphite-SiC, is favored under equilibrium conditions at solar and subsolar metallicities between ∼10⁻⁵and 10⁻⁸bar total pressure within circumstellar envelopes of carbon stars with nominal C/O = 1.2. We also explored the dependence of the sequence at C/O ratios of 1.1 and 3.0, and found that as the C/O ratio increases, the TiC-graphite-SiC condensation sequence region occurs toward higher total pressures and lower metallicities. 

Discussion of dust mineralogy and condensation temperatures of presolar grains forming in asymptotic giant branch (AGB) stars and in supernovae. Condensation temperatures as a function of total pressure and metallicity are listed for solar-like composition system. Reduced condensates at high C/O ratios are described. 

{"Abstract":["Machine-readable tables accompany the book chapter "Chemical Composition of the Sun", authors Maria Bergemann, Katharina Lodders, Herbert Palme,  Encyclopedia of Astrophysics 1st Edition (edited by I. Mandel, section editor F.R.N. Schneider) to be published by Elsevier as a Reference Module, 2025"]} 

We review a large body of available meteoritic and stellar halogen data in the literature used for solar system abundances (i.e., representative abundances of the solar system at the time of its formation) and associated analytical problems. Claims of lower solar system chlorine, bromine and iodine abundances from recent analyses of CI-chondrites are untenable because of incompatibility of such low values with nuclear abundance systematics and independent measurements of halogens in the Sun and other stars. We suspect analytical problems associated with these peculiar rock types have led to lower analytical results in several studies. We review available analytical procedures and concentrations of halogens in chondrites. Our recommended values are close to pre-viously accepted values. Average concentrations by mass for CI-chondrites are F = 92 ± 20 ppm, Cl = 717 ± 110 ppm, Br = 3.77 ± 0.90 ppm, and I = 0.77 ± 0.31 ppm. The meteoritic abundances on the atomic scale normalized to N(Si) =106 are N(F) = 1270 ± 270, N(Cl) = 5290 ± 810, N(Br) = 12.3 ± 2.9, and N(I) = 1.59 ± 0.64. The meteoritic logarithmic abundances scaled to present-day photospheric abundances with log N(H) = 12 are A(F) = 4.61 ± 0.09, A(Cl) = 5.23 ± 0.06, A(Br) = 2.60 ± 0.09, and A(I) = 1.71 ± 0.15. These are our recommended present-day solar system abundances. These are compared to the present-day solar values derived from sunspots of N(F) = 776 ± 260, A(F) = 4.40 ± 0.25, and N(Cl) = 5500 ± 810, A(Cl) = 5.25 ± 0.12. The recommended solar system abundances based on meteorites are consistent with F and Cl abundance ratios measured independently in other stars and other astronomical environments. The recently determined chlorine abundance of 776 ± 21 ppm by Yokoyama et al. (2022) for the CI-chondrite-like asteroid Ryugu is consistent with the chlorine abundance evaluated for CI-chondrites here. Historically, the halogen abundances have been quite uncertain and unfortunately remain so. We still need reliable measurements from large, representative, and well-homogenized CI-chondrite samples. The analysis of F, Br, and I in Ryugu samples should also help to obtain more reliable halogen abundances. Updated equilibrium 50 % condensation temperatures from our previous work (Lodders, 2003; Fegley and Schaefer, 2010; Fegley and Lodders, 2018) are 713 K (F), 427 K (Cl), 392 K (Br) and 312 K (I) at a total pressure of 10^ 4 bar for a solar composition gas. We give condensation temperatures considering solid-solution as well as kinetic inhibition effects. Condensation temperatures computed with lower halogen abundances do not represent the correct condensation temperatures from a solar composition gas. 

Lithium’s story spans the history of the universe and is one that links to all its largest-scale processes: big bang nucleosyntheses, the evolution of stars, and galactic chemical evolution. Lithium was the only metal produced in the big bang, alongside the gases H and He. Stars destroy both stable isotopes of Li easily, yet we still have Li today, even after generations of stars have come and gone. Ongoing production of Li by galactic cosmic rays and by a limited number of Li-producing nuclear reactions and transport processes in some rare types of stars keeps lithium present in the universe. 

Extensive experimental studies show that all major rock-forming elements (e.g., Si, Mg, Fe, Ca, Al, Na, K) dissolve in steam to a greater or lesser extent. We use these results to compute chemical equilibrium abundances of rocky-element-bearing gases in steam atmospheres equilibrated with silicate magma oceans. Rocky elements partition into steam atmospheres as volatile hydroxide gases (e.g., Si(OH)4, Mg(OH)2, Fe(OH)2, Ni(OH)2, Al(OH)3, Ca(OH)2, NaOH, KOH) and via reaction with HF and HCl as volatile halide gases (e.g., NaCl, KCl, CaFOH, CaClOH, FAl(OH)2) in much larger amounts than expected from their vapor pressures over volatile-free solid or molten rock at high temperatures expected for steam atmospheres on the early Earth and hot rocky exoplanets. We quantitatively compute the extent of fractional vaporization by defining gas/magma distribution coefficients and show that Earth's subsolar Si/Mg ratio may be due to loss of a primordial steam atmosphere. We conclude that hot rocky exoplanets that are undergoing or have undergone escape of steam-bearing atmospheres may experience fractional vaporization and loss of Si, Mg, Fe, Ni, Al, Ca, Na, and K. This loss can modify their bulk composition, density, heat balance, and interior structure.