The regular pattern of atoms, ions, or molecules in a crystalline substance. A crystal lattice can be regarded as produced by repeated translations of a unit cell of the lattice. See also crystal system.
http://cst-www.nrl.navy.mil/lattice/index.html An interactive version of the structures of a range of crystals from a US Navy website
http://www.geo.ucalgary.ca/~tmenard/crystal/crystal.html crystal models from the University of Calgary