The Oxidation-Reduction Potential in Geology

1 The Principal Methods of Determining Oxidation - Reduction Conditions.- The Fe../Fe... Ratio and Eh.- The Forms of Sulfur as Indicators of Oxidation - Reduction Conditions.- The Relationship of Organic Matter in Sediments and the Oxidation - Reduction Potential.- Iron-Mineral Indicators of Oxidation - Reduction Conditions.- Garrels' Thermodynamic Diagrams.- Other Methods of Determining Oxidation-Reduction Conditions.- 2 Thermodynamic Principles for Investigating the Conditions of Mineral Formation.- The Solubility of Compounds and the Maximum Work of a Reaction.- The Concept of the Oxidation-Reduction Potential.- Analysis of Some Errors.- 3 Stability Diagrams of Iron Minerals.- Stability Boundary of the Natural Environment.- The System Fe(OH)3-Fe3O4-Fe(OH)2.- The System Fe(OH)3-Fe3O4-Fe(OH)2 + CO2.- The Appearance and Behavior of Sulfide Ions in Sediments.- Mineral Forms of Iron Sulfides in Sedimentary Rocks and Recent Sediments.- Stability Diagrams of Sulfides.- 4 Conditions for Formation of Iron Minerals during Sedimentation and Diagenesis.- Change of pH during the Diagenesis of Sediments.- Change of Oxidation - Reduction Potential during Diagenesis of Sediments.- The Distribution of Hydrogen Sulfide.- Analysis of Mineral Formation.- Indicators of Oxidation - Reduction Conditions under Which Sedimentary Rocks Form.- Conclusions.- Literature Cited.