The second edition of this classic book provides an updated look at crystal field theory - one of the simplest models of chemical bonding - and its applications. Crystal field theory provides a link between the visible region spectra and thermodynamic properties of numerous rock-forming minerals and gems that contain the elements iron, titanium, vanadium, chromium, manganese, cobalt, nickel or copper. These elements are major constituents of terrestrial planets and significantly influence their geochemical and geophysical properties. A unique perspective of the second edition is that it highlights the properties of minerals that make them compounds of interest to solid-state chemists and physicists as well as to all earth and planetary scientists. This book will be useful as a textbook for advanced students as well as a valuable reference work for all research workers interested in this subject.

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In an effort to determine the nature and significance of the iron oxide mineralogy on Mars, reflectance spectra of eight polymorphs of FeOOH and Fe2O3 are presented together with additional data on these materials. The Kebulka‐Munk theory is used to qualitatively constrain the effect of other components that might interfere with iron oxide absorption features. Although the wavelength range 0.4–1.0 μm is potentially the most diagnostic spectral region for delineating the iron oxide phases, the effect of temperature complicates the identification of a given Fe3+ phase based on the position of the 6A1→4T1 absorption feature. The Fe3+ crystal field transitions are spin forbidden, but most of the iron oxide polymorphs exhibit anomalously intense crystal field absorption features resulting from magnetic coupling between adjacent FeO6 octahedra. The resulting deviations from observed remote sensed reflectance spectra of Mars may provide a basis for the exclusion of many iron oxide phases as significant components of the Martian Fe3+ mineralogy. Comparison with the visible region spectra of Martian bright regions suggest that the predominant Fe3+‐bearing phase may be a magnetically disordered material. Possible candidates include amorphous gels, some ferric sulphates, and other minerals in which Fe3+ ions in the crystal structure are not magnetically coupled.

Evidence is presented for the possible formation and existence of ferric sulfato complexes and hydroxo ferric sulfate minerals in the permafrost on Mars. Acidic groundwater, derived from atmospheric oxidation of volcanogenic H2S to H2SO4 aerosols, promoted chemical weathering of fayalitic olivines, iron‐rich pyroxenes, plagioclase feldspar, and pyrrhotite‐pentlandite mineral assemblages in crustal ultramafic and basic igneous rocks. The acidic groundwater entered into electrochemical reactions with the iron sulfides, yielding dissolved FeSO4+, Fe(SO4)2−, and FeOH2+ complex ions, and the precipitation of basic ferric sulfate minerals such as those belonging to the roemerite, copiapite, botryogen, and jarosite‐alunite groups. These phases are stabilized at low temperatures and pH in Martian permafrost. The occurrence of jarosites in terrestrial arid regions suggests that they could also survive on the surface of Mars. Melting of the permafrost and raising of the pH may have initiated the hydrolysis of dissolved ferric sulfato complex ions and led to the precipitation of FeOOH, which reacted with precipitated silica to form phyllosilicates. Alternatively, degradation of the hydrolysate FeOOH to Fe2O3 during sublimation of permafrost exposed on Mars' surface may account for the presence of eolian maghemite suspected to be the magnetic mineral observed on the Viking Landers.

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