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Samples obtained out of a carbonate concretion from the upper Olentangy shale were analysed using x-ray methods and insoluble residue techniques. Determined were composition, the Fe content, the Sr content, and the percent insoluble residue. The carbonate mineral in the concretion was identified by x-ray diffraction to be ferroan dolomite. This finding contradicts a much earlier attempted chemical study of a concretion from the lower Olentangy shale that found calcite to be the main carbonate mineral. The calculated average concentration of the other minerals and clay minerals present in the concretion is given below in units of percent: Ferroan Dolomite---------- 69.41 Quartz-------------------- 8.3 Illite -------------------- 14.00 Kaolinite & Chlorite ------ 4.10 Others*-------------------- 4.19 TOTAL 100.00 *Pyrite, Montmorillonite, and other mixed-layer clays. It was concluded that the concretion was fairly homogeneous in its Sr content, and in its Fe content when corrected for the pyrite that caused higher values for Fe on the outside and in the center. The concentration of FeO in the samples was compatable with those values of FeO in ferroan dolomites given by Deer, Howie, and Zussman (1962). The concretion showed a decrease in the carbonate content toward the outside, with the insoluble residue content increasing in the same direction. This is perhaps due to the occurrence of pyrite here, or by the assimilation of sediments on compaction.