A large proportion of the aragonite oolites forming at present in the Great Salt Lake, Utah display a peculiar type of fibro-radiated structure generated during their seasonal inversion to calcite. The recrystallization insteacl of being uniformly distributed in the spheroidal bodies has preferentially taken place along certain radii generating wedge-like bundles of clear calcite fibers separated by intermediate areas of dark cryptocrystalline calcite enriched with clay impurities. The final result in cross section is to change the original circular outline of the concentric rings into a juxtaposition of convex and concave segments self-perpetuating from one season to another. The name of cerebroid oolite is applied to these peculiar bodies which are the modern equivalents of similar forms described in the Ste. Genevieve Formation (Mississippian) of Illinois and adjacent states. It is suggested that the differential recrystallization which generated cerebroid oolites in the past may not necessarily have been restricted to oolites originally aragonitic.