A crystallite's a domain of solid-state matter that's the same structure as a single crystal. Metallurgists often refer to crystallites as "grains". Solid objects that're large enough to see and handle are rarely composed of a single crystal, except for a few cases (gems, silicon single crystals for the electronics industry, certain types of fiber, and single crystals of a nickel-based superalloy for turbojet engines). Most materials are polycrystalline; they're made of a large number of singl… (More on Crystallite)