Robert F. Mueller

Energetics of HCl and HF in volcanic emanations

Abstract Comparison of the fugacities of HCl and HF calculated from thermochemical data with the abundance of these gases in fumarolic emanations indicates undersaturation of the magma with respect to NaCl, CaSiO3 and Al2SiO5 and that the gases have been quenched from magmatic temperatures.

Kinetics of CO2 production on venus

Abstract Consideration of theoretical limits and experimental data for the kinetics of the reaction quartz + calcite → wollastonite + CO 2 supports the concept of a shortterm quasiequilibrium state for the atmosphere of Venus. These data indicate that the time scale of this reaction and of any competing CO 2 producing reaction may be as short as several hundred years or less at the inferred Venus surface temperatures.

Planetary Probe: Origin of Atmosphere of Venus

The high temperatures and chemical composition, as determined by space probe and terrestrial observation, suggest that the present atmosphere of Venus has formed by chemical interaction with the lithosphere. Although the precise reactions have not been identified, good theoretical approximations to the molecular abundance may be obtained from reactions applicable to terrestial rocks. The high temperatures and chemical reactivity create conditions on Venus which are fundamentally different from those on the cooler terrestrial planets where the attainment of equilibrium is prevented by kinetic barriers.

Partitioning of cations between coexisting single- and multi-site phases: A discussion

Abstract Chemical potentials of atoms or ions on nonequivalent lattice sites have no validity because these particles cannot be considered independently variable components. Orthopyroxene does not in general exhibit ideal mixing on individual sites. Also a corrected form of the mean molar free energy is presented.

The energetic basis

The foundation of the energetic approach to mineral systems is provided by the laws of thermodynamics. These laws are broad generalizations that apply to all forms of matter, and in principle no system is too complex to yield to their application if the required data are available. However, in many problems of mineral chemistry in which complex phases are involved, the equations of thermodynamics cannot be directly applied to obtain quantitative results. The reason for this is that they give us relations only in their implicit forms and what we require are the equations of state of the phases that lead to explicit functions linking the intensive variables such as temperature, pressure, and composition. These equations of state may be based on empirical data or upon theoretical models, which usually have their foundation in statistical mechanics. Thus we shall be concerned with deducing activity coefficients that give us a measure of the deviation of a phase from the simplest model—that of an ideal solution.

Metamorphism and metamorphic mechanisms

We made a brief reference to metamorphism of meteorites in Chapter 6. Metamorphic rocks constitute an important part of the Earth’s crust. During the last two decades very significant progress has been made in the experimental techniques for the study of rock systems. Particularly notable in this regard is the development of high-pressure techniques, the electron-microprobe analyzer for chemical analysis, and the sophisticated methods of studying solid-gas equilibria with controls of fugacities of O2, CO2, and H2O. Theoretical work has been concerned with the method of graphical representation of mineral assemblages, application of Schreinemaker’s method of analysis of phase equilibrium, the nature and composition of crystalline and fluid solutions, and the treatment of open and closed systems during metamorphism. As a result of the various experimental and theoretical studies (see reviews by Hewitt and Wones, 1971; Winkler, 1974), our understanding of terrestrial metamorphism has improved tremendously over the last decade.

Classifications of rocks

There is nothing very exciting about rock classifications, yet petrology could scarcely do without them. Classifications take many forms, and so we may justify them in various ways. Some, based on such characteristics as color, are useful chiefly in the field and will not concern us further here. Again, classification based on texture and implicit in such rock names as diabase will be of only secondary interest. We shall be concerned chiefly with the chemical and mineralogie classifications that aid us in summarizing much diverse

The terrestrial planets

The terrestrial planets present us with a sequence of widely varying physical environments that determine their chemical and petrologic characteristics.

Differentiation and crystallization of magmas

The conclusion that the common igneous rocks form continuous series with respect to bulk compositional variation was an outgrowth of the detailed investigations of the nineteenth century petrographers. However, an understanding of the full evolutionary meaning of these series, in particular with respect to physical chemistry, did not come until the turn of the century. The groundwork for this interpretation was laid by such investigators as Michel-Levy and J. H. L. Vogt and was carried forward by the careful experimentation and solid deductions of N. L. Bowen and his associates. The ground broken by these early investigators is still being explored today, and recent work has revealed some important facets which were virtually ignored by these and even most comparatively recent investigators as well. One of the most important of recent developments is a growing appreciation of the effect of oxidation, while another is concern with the effect of high total pressures on crystallization, partial melting, and differentiation, with particular reference to the origin of basaltic (or gabbroic) and andesitic magmas. Today these two topics are among the most active areas of petrologic research.

Igneous plutons: Their physical chemistry and mode of occurrence

Our topics here are the physical chemistry of the rocks and magmas and the structural modes of occurrence of the prominent plutonic bodies as illustrated by specific examples from the literature. However, it is desirable first to consider the observed range of chemical composition of those bodies. The primacy of composition, which we have previously emphasized for metamorphic rocks, compels us again to settle the question of the compositional fields of stabilities of magmatic minerals before it is possible to discuss meaningfully the contributions of temperature and pressure. Our concentration on plutonic rocks is dictated not only by their relative importance in the evolutionary scheme but also by their registering with greater fidelity than volcanics the physicochemical environment of the deep-seated regions in which differentiation occurs.