(N/A) Based on the study of crystals,it can be concluded that the shape of any crystal belongs to one of the seven regular shapes. These basic regular shapes are known as the seven crystal systems.
To determine which system a given crystal belongs to,one must measure the angles between the faces and the number of axes required to define the unit cell.
The seven crystal systems are:
$1$. Cubic: $a = b = c$ and $\alpha = \beta = \gamma = 90^{\circ}$
$2$. Tetragonal: $a = b \neq c$ and $\alpha = \beta = \gamma = 90^{\circ}$
$3$. Orthorhombic: $a \neq b \neq c$ and $\alpha = \beta = \gamma = 90^{\circ}$
$4$. Monoclinic: $a \neq b \neq c$ and $\alpha = \gamma = 90^{\circ}, \beta \neq 90^{\circ}$
$5$. Hexagonal: $a = b \neq c$ and $\alpha = \beta = 90^{\circ}, \gamma = 120^{\circ}$
$6$. Rhombohedral (Trigonal): $a = b = c$ and $\alpha = \beta = \gamma \neq 90^{\circ}$
$7$. Triclinic: $a \neq b \neq c$ and $\alpha \neq \beta \neq \gamma \neq 90^{\circ}$