Mined since prehistoric times, oolitic ironstones (OIS) were a very important world source of iron from 1850 to 1945: hereafter they have been progressively replaced by the Precambrian Banded Iron- Formations (BIF). OIS are iron-rich sedimentary rocks bearing ferruginous ooids. They consist of at least 15% iron. In Western Europe, their overall depositional environment is that of a shallow shelf, most often located close to the transition from non-marine to marine environments. Their main age range is concentrated within the Ordovician through Devonian and the Jurassic through Paleogene. Proterozoic occurrences are known but these occur outside Europe. The host rocks of the ironstones are predominantly clastic, whereas the host sediment of the ferruginous ooids can be either clastic or carbonate or both. The OIS occur at the top of coarsening and shoaling upward cycles. They represent condensed deposits and transgressive system tracts. Numerous oolitic ironstone deposits are interpreted as tempestites or as intertidal deposits. It is generally agreed that ferruginous ooids formed in shallow marine water conditions, near the water-sediment interface, with repeated reworking of the sediment. Such an environment implies oxidizing conditions, the sedimentary iron being in the ferric state. The exact source of the iron is still a matter of discussion and speculation, just as the primary or secondary origin of the ferruginous ooids. Besides hematite (or goethite), also siderite, Fe-dolomite and berthierine/chamosite are present in the OIS as iron-bearing minerals. Due to weathering processes the carbonate matrix is often removed, the iron is released and oxidized, whereas the ferrous silicates are converted into ferric oxides or ferric hydroxides. Many old mining activities are based on occurrences of this weathered ore. The latter material has also strong staining properties. 1. Germany OIS are outcropping in the Eifel area. The latter is part of the Ardenno-Rhenish Massif and lies in the eastern extension of the ...