Goethite stability and the origin of red beds

Abstract

The differential solubility of hematite and goethite in 0.1 M HCl has been determined at 85°C. From this, calculations show that finely divided limonitic goethite is thermodynamical unstable relative to hematite plus water under practically all geological conditions. This indicates that many ancient red sediments could have been originally yellow and that the red color could have developed diagenetically even during shallow burial at low temperatures. The data also indicate that limonitic goethite should be thermodynamically unstable on the surface of Mars.