X-ray diffractions, in addition to fundamental diffractions, which appear as an alloy inverts from disorder to perfect order of its constituent atoms at lattice sites; called superlattice diffractions and attributed to a superstructure of ordered atoms. Superlattice diffractions also appear where long-range order obtains in the stacking of silicate structural units, such as in phyllosilicates. See: superstructure; long-range order.