A uranium-bearing unit, stratigraphically classified as Lower Ordovician, is included in the border sedimentary sequence of the Swedish Caledonides at Tåsjö, Västernorrland County. The parts of the sedimentary rocks rich in uranium are characterized by the mineral association glauconite, calcite, siderite, dolomite, carbonate-fluor-apatite (marine apatite), and quartz. Most of the uranium is localized in the mineral apatite. Investigations of the way in which this mineral occurs in the rocks indicate that the uranium is syngenetic with the deposition of the sediment and the formation of the apatite.