Study of 13 oolite samples from Great Salt Lake, Utah by means of X-ray analysis, staining for aragonite with Feigl's solution, and the use of scanning and petrographic microscopes show that aragonite makes up all or more than 90% of the carbonate mineralogy of the samples. This new evidence, combined with the high degree of allochem recrystallization, indicates that the aragonite in the allochems typically undergoes recrystallization to aragonite and not to calcite as interpreted by Eardley (1938) and Carozzi (1962). Failure to take note that the original grain orientation in the rim of Great Salt Lake ooids is radial (Eardley, 1938), along with confusion about the meaning of the term structure as applied to ooids, has conceivably retarded a better understanding of ooid genesis and diagenesis. Radial grain orientation is demonstrably not developed in many initially aragonitic Pleistocene marine ooids as a result of their partial to complete conversion to calcite. Many ooids in marine limestone probably formed initially with an entirely radial grain orientation in their rims under a variety of environmental conditions. This hypothesis provides an alternative to the popularly accepted hypotheses that all ooids in marine limestone were initially like those that occur today in the Bahamas and Persian Gulf, and that radial grain orientation in ooids is invariably a product of diagenesis.