1.   The crystal lattice is composed of a basic unit called a unit cell.

2.   The unit cell is repeated throughout the crystal.

3.   There are only seven types of unit cell.

4.   These unit cells are sometimes called primitive unit cells or crystal systems.

5.   Simple cubic, for example, is a primitive unit cell.

6.   The face-centred cubic lattice consists of a system of intersecting simple cubic unit cells.

7.   The body-centred cubic lattice consists of interpenetrating simple cubic unit cells.