A scale of values, measured as electric potential in volts, indicating the ability of a substance or solution to cause reduction or oxidation reactions under non-standard conditions. The term is sometimes used interchangeably with the term oxidation potential, but in either case the symbol E^θ‎ would refer to standard conditions, while E_H signifies non-standard conditions, usually processes in natural systems such as sea water or soils. The higher the value of E_H, the more oxidizing the conditions. The redox potential is important in weathering in terms of oxidation and reduction; if the environment will accept electrons it can precipitate Fe(OH)₃, if not the Fe²⁺ ions will remain in solution. Values in natural environments are closely linked, and vary, with changes in pH.