The formation of sedimentary iron minerals

An attempt to combine laboratory and field data on recent sedimentary environments to produce mineral stability diagrams suggests that two distinct situations may be recognized. In depositional water, only ferric compounds can be truly stable. In interstitial water, beneath the sediment-water interface, ferrous compounds (pyrite, pyrrhotite, magnetite, siderite, and chamosite) are stable. Anion activity (sulfide and carbonate) appears to be the most important chemical control. The theoretical findings (Pt. 1 by C. D. Curtis) are consistent with interpretation of petrographic observations on Carboniferous and Jurassic ores of the British Isles (Pt. 2 by D. A. Spears).