Modern materials are complex and their investigation demands advanced characterization tools capable of elucidating their structure in three dimensions without the need for complicated sample preparation. Herein, we discuss our implementation of diffraction/scattering computed tomography (DSCT). DSCT is based on the use of diffraction information for tomographic reconstructions rather than linear attenuation as in regular μ-CT. This provides much additional information on the material under investigation. We illustrate the use of DSCT by discussion of data on a biomineralized attachment organ from a marine mussel. DSCT allowed mapping the spatial distribution of calcium carbonate polymorphs aragonite and calcite even though they were indistinguishable in absorption tomography. Detailed analysis of reconstructed diffraction patterns may provide additional insights as exemplified in the present case by mapping of the degree of chemical substitution in calcite.