In order to describe the nature of the wall, all that needs to be specified is the character of the brick and how it is arranged.
The shape of the unit cell is described in terms of the lengths of the cell edges and angles between the cell edges. The unit cell contents are specified in terms of where individual atoms are located within this volume.
Minerals belonging to the same crystal system have the same shaped unit cell cell. The lenghts of the edges of the unit cell vary depending upon the types of atoms and how they are arranged.
Many important physical characteristics important to orientation and faceting of gems follow from the mineral's symmetry.