- © 2000 Mineralogical Society of America
Oxygen is the most abundant element in the Earth, constituting about 43 percent by weight of the crust and mantle. While most of this mass is incorporated into silicates, the next most abundant mineral group in the planet is the oxides. The oxide minerals are generally considered to be those oxygen-based minerals that do not contain a distinct polyanionic species such as OH−, CO32−, SO42− PO43−, SiO44−, etc. The oxide structures are also of interest in mineral physics, because, at high pressure, many silicates are known to adopt structures similar to the dense oxides (see Hazen and Finger, this volume).
Oxide minerals, because of their compositional diversity and structural simplicity, have played a special role in the development of comparative crystal chemistry. Many of the systematic empirical relationships regarding the behavior of structures with changing temperature and pressure were first defined and illustrated with examples drawn from these phases. Oxides thus provide a standard for describing and interpreting the behavior of more complex compounds. Our principal objectives here are to review the mineral structures that have been studied at elevated temperatures and pressures, to compile thermal expansion and compression data for the various structural elements in a consistent fashion, and to explore systematic aspects of their structural behavior at nonambient conditions. The large and growing number of single-crystal structure investigations of the simpler or more important dense oxides at high pressures and temperatures warrant this comparative synthesis.
Regarding thermal expansion for various structural elements, we have chosen to assume linear expansion coefficients. This approach facilitates comparison across disparate structures and methodologies, and it reflects the reality that data are not sufficiently precise in many cases to permit the meaningful derivation of second-order thermal expansion parameters. For compression …