Rock-forming minerals. Non-silicates. Oxides, hydroxides and sulphides / Породообразующие минералы. Несиликаты. Оксиды, гидроксиды и сульфиды

Tt is 50 years since the publication of the first edition of this volume of Rock-forming Minerals. The intervening years have seen a vast growth in the range and quantity of published work on 'non-silicate" rock-forming minerals, a growth that has justified dividing the topics of the first edition into two volumes (sulphates, carbonates, phosphates and halides have already been covered; see Chang, Howie and Zussman, Rock-forming Minerals, Vol. 5B, 2nd edn. The Geological Society, 1996). Here, we discuss the oxides, hydroxides and sulphides. This growth in published information on oxide, hydroxide and sulphide minerals has resulted partly from the availability of new techniques for the chemical and structural analysis of these materials and the characterization of their physical and chemical properties. It has also been the result of the opening-up of entirely new fields of investigation where these minerals play a key role. The list of minerals discussed in this new edition has expanded somewhat compared with the first edition; although the same five sulphide minerals are considered "rock-forming', the hydroxides have gained several new iron hydroxide phases (akaga-neitc. ferrihydrite and feroxyhyte), while losing limonite. These developmenb are largely due to better characterization of poorly crystalline ultrafine particle phases using new techniques. The list of oxides has also expanded with additions including quandilite. pseudonitile and armalcolite, the last a lunar mineral and a legacy of the Apollo missions which occurred seven years after publication of the first edition.

The majority of the minerals discussed in this volume are opaque and, therefore, not suited to examination in transmitted light (in thin section), but requiring examination in reflected light (polished section). Although the techniques of reflected light microscopy, sometimes termed 'ore microscopy', are less widely taught than in the past, their importance cannot be over-emphasized. Qualitative observations using these techniques provide essential information on textural and paragenetic relationships involving the opaque minerals.

Quantitative reflected light microscopic studies, particularly involving the measurement of reflectance (and, in some cases, quantitative colour and Vickers microhardness) offer a simple and cost effective means of mineral identification and characterization. For this reason, quantitative reflected light microscopy data are provided in the opening section for each mineral where appropriate.

The crystal structures of the minerals discussed here are amongst the few aspects where the basic information was largely available at the time of the first edition. Structures have been further refined using X-ray diffraction, and the transmission electron microscope used to great effect to study poorly crystalline phases, superstructures and complex intergrowths. Entirely new areas of investigation have centred upon investigating the structures (and hence reactivities) of the mineral surfaces, investigations made possible by new imaging methods such as scanning tunnelling and atomic force microscopies. New spectroscopic methods, for example X-ray photoelectron, have faciliiated chemical analysis of surfaces and surface reaction products, enhancing our understanding of how these minerals transform through processes such as oxidation. Another key area which has only developed since the 1970s concerns the electronic structures (or 'chemical bonding') of these minerals. Using various spectroscopic methods, and through the application of quantum mechanical calculations enabled by advances in computing, it has now become possible to predict crystal structures, stabilities and a range of physical properties of simple minerals from first principles.

The chemistries of the minerals discussed in this volume, and their phase relations, have been extensively studied in the decades since publication of the first edition.

Analysis of the natural minerals has been revolutionized through application of the electron microprobe and related microbeam methods which have enabled micron-scale analytical resolution. Laboratory experiments have provided the data to establish phase relations in nearly all binary, ternary and many more complex systems of relevance to the Earth and materials sciences. Particularly important have been the advances in studying phase transformations at ultra-high pressures. Several of the minerals discussed here are a major focus of high-pressure research because of their perceived importance as constituents of the Earth's deep interior.Certain physical properties of the oxides and sulphides have also been much studied because of their geophysical importance. This is true of electrical and, particularly, magnetic properties. The iron oxides dominate the fields of geomagnetism and palaeomag-netism, and sulphides such as pyrrhotite also play an important role. The electrical and magnetic properties of these materials have also led to many technological applications.
Finally, the information summarized in the following pages under the heading of 'paragenesis' is but a brief survey of the vast body of data now available to describe the occurrence of oxides, hydroxides and sulphides in rocks, ores and sediments, and to elucidate their processes of formation. Such processes have been clarified not only by the knowledge provided by data such as that on phase relations, but also by the evidence from stable isotope geochemistry. This now includes data from isotopes of oxygen and sulphur and also from the transition metals. Compositional and isotopic studies of oxide and sulphide minerals in meteorites and other extra-terrestrial materials have shed light on the formation and evolution of the solar system. At the other extreme, the importance in Earth surface systems of many of these minerals, particularly the iron hydroxides and sulphides, is only now being fully appreciated. For example, they can play a critical role in the transport or entrapment of pollutants, whether those pollutants are heavy metals, radionuclides or organic molecules.
Even in a substantial volume, it is impossible to cover all aspects of the literature dealing with the 'rock-forming' oxide, hydroxide and sulphide minerals. It is especially difficult for these groups of minerals because many of them are of major research interest to scientists working in fields as diverse as solid-state physics, materials science, inorganic chemistry and mineral technology as well a* in the Earth and mineral sciences. In what follows, we have aimed to provide the essential information of interest to mineralogists, petrologists and geochemists, but hope to attract a wider audience. Inevitably, beyond the core content, the present work partly reflects the particular interests of the authors,.