Abstract Under crossed electric and magnetic fields, multiply coated microspheres form columnar crystallites with an internal structure that transforms from body-centered-tetragonal to face-centered-cubic as the ratio between the magnetic and the electric fields exceeds a minimum value. The observed transition scenario is in excellent agreement with calculations. These multiply coated microspheres also serve as building blocks for photonic crystals. Robust photonic gaps exist in any periodic structure built from such spheres when the filling ratio of the spheres exceeds a threshold.