Computed X-ray microtomography (CMT) was used to construct 3-dimensional images of four different rock materials: Jurassic laminated sandstones from the Towaco Formation (Newark Supergroup) in New Jersey; manganese encrusted, Cretaceous reef limestone dredged from Wodejebato Guyot (northern Marshall Islands); Eocene foraminiferal limestone from Limalok Guyot, (southern Marshall Islands); and a fragment of carbonaceous chondrite. CMT analysis was done using beamline X27a at the National Synchrotron Light Source, Brookhaven National Laboratory. The digital CMT images, with resolutions between 3.4 and 6.8 microns, effectively reveal the amount and structure of porosity in the sandstones and limestones. Lamination orientations are apparent in the sandstones since each lamina has a different porosity. Moldic porosity in the foraminiferal limestone can be imaged in 3-dimensions using CMT. This technique may be useful in assessing diagenetic history in the case of the limestones and depositional history in the case of the sandstones. The ability to accurately assess the sizes, shapes and connectivity of porosity has important implications for hydrogeology and petroleum geology. The absorbance contrast between different rock components within the Cretaceous limestone and the meteorite fragment allow imaging of the sizes, shapes and orientation of inclusions within the meteorite as well as the distribution of manganese oxide within the limestone. Rock components with similar absorbance, such as the unaltered fossils within the limestone samples, were not successfully imaged using this technique.