The extensive use of zeolites and their impact on the world's economy has resulted in many efforts to characterize their structure and improve the knowledge base for nucleation and growth of these crystals. Zeolite crystal growth (ZCG) experiments have been conducted in space by many researchers. The results have been varied with little overall constancy with respect to the types of zeolites grown, the procedures used, and methodologies employed for comparison of terrestrial and microgravity processed crystals. Results from this laboratory have indicated that solutions must be mixed in space, and that the nucleation mechanism as well as the growth mechanism is affected by the “suppression” of fluid motion. Earlier flight experiments (STS-43, STS-50 and STS- 57) indicated that by controlling the nucleation event, the size of the crystals could be increased with improved structural quality compared to the ground-based controls. This was hypothesized to be the result of hindrance of the solution/dissolution mechanism caused by reduced fluid motion. USML-2 (STS-73) zeolite experiments were designed to further enhance the understanding of nucleation and growth of zeolite crystals, while attempting to provide a means of controlling the defect concentration in microgravity. Zeolites A, X, and Silicalte were grown during the 16-day United States Microgravity Laboratory number 2 (USML-2) mission. All zeolites were successfully grown in the 16 day mission. The zeolite A and X crystals were in general larger in dimension (10-50%), but not substantially different in crystal perfection as measured by their lattice parameters. However, They were significantly smoother as indicated by AFM. Zeolite β as well as Silicalite were only slightly larger in size but, appear to have different distributions of Aluminum atoms as determined by selective catalytic reactions.