Particles can be made up of one or more crystallites with different orientations. If the crystallite is the same size as the particle, the particle is called monocrystalline. If the crystallite is smaller than the particle, i.e. when the particle is made up of more than one crystallite, it is classified as polycrystalline. For this reason, there can be differences between the size of the crystallite and the size of the particle in a material .