Oxygen fugacity

Oxygen fugacity is a thermodynamic measure of oxygen’s effective chemical potential, expressed as an equivalent pressure. In geological systems, it helps determine which oxidation states and iron-bearing minerals are stable.

Chemical potential: A thermodynamic quantity measuring how a system’s energy changes when a substance is added. Oxygen fugacity expresses oxygen’s chemical potential in pressure-like form.
Magma redox state: The oxidation-reduction condition of a magma, commonly described by its oxygen fugacity. It links oxygen fugacity to mineral formation and volcanic processes.
Thermodynamic activity: A dimensionless measure of a substance’s effective concentration in a non-ideal system. Activity explains why chemical potential is not determined by concentration alone.
Oxygen partial pressure: The pressure contribution of oxygen in a gas mixture. It approximates oxygen fugacity only when oxygen behaves nearly ideally.
Fugacity: An effective pressure that accounts for non-ideal behavior in a gas or fluid. Oxygen fugacity applies this thermodynamic correction specifically to oxygen.
Mantle redox state: The oxidation-reduction condition of Earth’s mantle, inferred from minerals and chemical equilibria. Mantle oxygen fugacity constrains volatile speciation and the stability of mantle minerals.
Partial pressure: The pressure a component of a gas mixture would exert if it occupied the volume alone. Oxygen fugacity is often reported as an equivalent oxygen partial pressure.
Redox potential: An electrical potential expressing the tendency of a system to accept or donate electrons. It describes redox conditions in a different framework from oxygen fugacity.
Oxygen buffer: A mineral assemblage or reaction that fixes oxygen fugacity under specified conditions. Buffers impose a reference oxygen fugacity on geological experiments and natural systems.
Peridotite: A coarse-grained ultramafic rock composed chiefly of olivine and pyroxenes. Its mineral equilibria record oxygen fugacity in the upper mantle.

Linked from 5 pages