Precipitation hardening analysis

Often iron stones have an oolithic texture, i.e. they consist of perfectly rounded bodies, the so-called ooids. Iron oxide ooids are mm to cm in size, hardened and showing concentric Fe accumulations (Plate 15.1), which suggest cyclic precipitation of the Fe oxide. Ghemical point analysis by the electron microprobe indicates enrichment of Ti, P and V in the Fe oxides, whereas Si and Al concentrations are very low (Fig. 15.5). The mode of Fe ooid formation and in particular the need for some mechanical action to produce the perfect rounding has been a matter for discussion for a long time. In principle, both terrestrial and marine formation is possible and it... 

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