Nature of Free Iron Oxides in Soil Clays

Abstract

A DIFFERENTIAL thermal analysis examination of soil clays at present in progress with the view of elucidating their mineral composition has provided some evidence regarding the nature of the iron oxide coatings on the clay micelles. One of the clays studied, which had a free iron oxide content of 31 per cent, had been separated from a C-horizon sample (depth 48–52 in.) of a soil developed on basic igneous till and had been treated several times with hydrogen peroxide on the steam-bath to remove organic matter. Its thermogram shows a strong exothermic peak at about 345° C. (curve 1 in the graph), which because of its sharp well-defined nature appears to be quite different from the broad, rather diffuse band usually associated with organic matter, but which bears a considerable resemblance to that quoted by Berg, Nikolaiev and Rode1 for ‘cold-precipitated’ or ‘glowing’ hydrated ferric oxide2.