Table 16.2 seven crystal systems or Bravais unit cells.

Sr no

Type/category cubic

Edge lengths

Internal angles

1

Cubic

a = b= c

= = = 90^o

2

Hexagonal

a = b c

= = 90^o, = 120^o

3

Tetragonal

a = b c

= = = 90^o

4

Rhombohedral

a = b = c

= =    90^o

5

Orthorhombic

a b c

= = = 90^o

6

Monoclinic

a b c

= = 90^o,  

7

Triclinic

a b c

          90^o