Mesoscale (secondary) structure arising from association of layered silicates is quantified and its impact, along with constituent interactions, on elevated temperature crystallite morphology in nylon-6/montmorillonite nanocomposites is examined. Simultaneous small- and wide-angle X-ray scattering and diffraction methods are developed to provide detailed information on the secondary structure of the layered silicate and the structure of the crystalline polymer in the presence of the layered silicate. Ultra-long range order (20-60 nm) of the inorganic layers is observed at low-volume fractions (0.8 vol%). Elevated temperature (205 degreesC) crystallite morphology of the nylon-6 matrix depends on the secondary structure and interfacial interactions. Smaller, more disordered lamellae are observed in the in situ polymerized nanocomposites whereas larger, more ordered lamellae are observed in melt-processed nanocomposites.