Ferruginous concretions around root channels in clay and fine sand deposits

Spherically layered ferruginous concretions formed in soils in Finland are described. The cementing iron-rich material is in an amorphic state and binds the loose detrital mineral grains of quartz, feldspars, amphiboles, etc. Electron microprobe analyses show that iron and manganese are present as concentric rings around the root channels but that calcium is evenly distributed. The highest manganese content is found near the channel as a dark almost black layer or spot, but around the centre, where the content of cementing materials decreases, iron predominates. The origin of these ferruginous concretions and the significance of redox conditions in soils during their formation are discussed.