the diamond crystal structure
belongs to the face-centered cubic lattice
, with a repeated two-atom pattern.
in crystallography, the terms crystal system, crystal family, and lattice system each refer to one of several classes of space groups, lattices, point groups, or crystals. informally, two crystals are in the same crystal system if they have similar symmetries, although there are many exceptions to this.
crystal systems, crystal families and lattice systems are similar but slightly different, and there is widespread confusion between them: in particular the trigonal crystal system is often confused with the rhombohedral lattice system, and the term "crystal system" is sometimes used to mean "lattice system" or "crystal family".
space groups and crystals are divided into seven crystal systems according to their point groups, and into seven lattice systems according to their bravais lattices. five of the crystal systems are essentially the same as five of the lattice systems, but the hexagonal and trigonal crystal systems differ from the hexagonal and rhombohedral lattice systems. the six crystal families are formed by combining the hexagonal and trigonal crystal systems into one hexagonal family, in order to eliminate this confusion.