The environmental control of sedimentary iron minerals

Economic Geology



An Eh-pH stability diagram is developed for hematite, magnetite, siderite, pyrite, and iron sulfide that indicates the relative position of their stability fields in a normal sea water system. With the exception of the magnetite-siderite relationship, Eh is much more critical than pH. In general terms, hematite is stable under oxidizing conditions, siderite and magnetite under intermediate to moderately reducing conditions, pyrite under moderate to strongly reducing conditions, and iron sulfide under still stronger reducing conditions. Because of numerous variables involved the relative positions of the stability fields are stressed rather than their limits on the Eh and pH scales. The inclusion of a magnetite field suggests that magnetite should be much more important as a primary or diagenetic mineral in sedimentary rocks than has been commonly recognized. This is in accord with numerous recent suggestions to that effect. The importance of thermodynamic equilibrium is stressed and it is suggested that differences in rates of formation of the various minerals and the persistence of some metastable phases are among the commonest causes of lack of equilibrium.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title The environmental control of sedimentary iron minerals
Series title Economic Geology
DOI 10.2113/gsecongeo.53.2.123
Volume 53
Issue 2
Year Published 1958
Language English
Publisher Society of Economic Geology
Description 18 p.
First page 123
Last page 140
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