The periodic table containers some 92 naturally occurring elements. Each element exhibits specific physical properties and characteristic atomic structure such as bond angle/length, atomic radii, valance, oxidation state etc., which can be combined in such a way as to generate a energy minimized structures that have a stable state. The mixtures of elements from the periodic table then generate 4,200 minerals in the earth's crust. Minerals divide into groups based on composition: silicates, carbonates, sulphides, sulphates and phosphates etc. The chemical basis for the formation of minerals are heat and pressure beneath, or sedimentation and weathering at or near the earths surface. The minerals are crystals at the microscopic level and may be formed to be completely homogenous, or in some cases can contain defects that are either localized or may be completely highly delocalised along crystal boundaries. These properties all contribute to the type and distribution of minerals on earth.
Oxygen is an important component of many minerals and forms a mineral subset termed the oxides. There are almost 600 oxides and for these minerals the and each element has an oxide.
Oxygen Fugacity
Mineralogy is the study of minerals and for the class of Oxides the abundance of oxygen plays a determinant role in formation. The expression commonly used for oxide formation is the term Oxygen Fugacity and is used to describe the oxygen concentration. Oxygen Fugacity, is essentially the same as the partial pressure of oxygen and is expressed f (O2) or the Log f (O2). The Oxygen Fugacity measurement is typically given in units of atmosphere and must be accompanied by a temperature. In the geochemical environment it is unlikely that the oxygen partial pressures are ever greater than air pressure (0.21 atm) and range down to Log(-60).
Experimentally the low Oxygen Fugacity concentrations are reached via the use of reactive gases in high temperature furnaces. Addition of oxidising gases such as CO2 and H2O and mixtures of reducing gases (CO or H2) are injected into a furnace (1000°C) near the oxide sample where the gases can react. At these high temperatures the container is also likely to succumb to the reaction unless materials such as Ag-Pd alloys, platinum wire and Fe-Pt alloys.
Oxygen Fugacities as a function of temperature
Figure 1: a Log Oxygen Fugacity vs Temperature for the relative stabilities of the various oxidation states of iron in the Fe-Si-O system: MH, magnetite-hematite; FMQ, fayalite-magnetite-quartz; QIF, quartz-iron-fosterite.
Ice
The di-hydrogen oxide is by definition a mineral although this comes as a bit of a surprise to some people. For an element to be classed as a mineral it must be a solid, and be comprised of a crystal lattice structure, naturally occurring and be homogenous. All these properties are features of ICE.
When frozen: hardness of 1.5 Mohs at 0°C and 6 Mohs at -70°C
Crystalline: Ic, hexagonal 6/m 2/m 2/m
Naturally occurring and homogenous: pure H2O.
Oxide Minerals A couple of web sites have extensive lists and details of the different oxides <link> <link>.
Oxide Mineral (2) Pictures <here> of many oxide minerals and a site with crystallographic structures of select oxides <Mineral Web>.
