Crystal basis:
The structure of the crystal is determined by:
1. Crystal Basis (Point group)
2. Lattice Geometry (Translational symmetry)
Together, the point group symmetry combined with the translational symmetry give the space group symmetry that is a characteristic property of each mineral. The crystal basis is the arrangement of atoms that is particular to the mineral being considered. Each of these basis units is called a unit cell. The unit cells are repeated over and over again in three dimensions to make up a macroscopic crystal.
The repeating units can be chosen to have different sizes, but the minimum size possible is the primitive unit cell. Larger unit cells are called doubly, triply, quardruply primitive.
