According to Bravais "three vectors and their angles study shows morphologically that the unit cells can be classified into seven crystal systems based on the presence of certain rotation axes. These seven crystal systems are classified according to geometrical and symmetrical considerations as

(i) Cubic

(ii) Orthorhombic

(iii) Rhombohedral

(iv) Monoclinic

(v) Triclinic

(vi) Tetragonal

(vii) Hexagonal

Bravais further showed that there would be only four possible ways in which constituent species of a unit cell can be arranged. They are

(a) Primitive or simple

(b) Body centred

(c) Face centred and

(d) End centred

So, the total number of possible unit cells are `7 xx 4 = 28`. Bravais, then went on to predict that out of these `28` possible unit cells, only `14` of them exist in nature. These fourteen unit cells that actually exist are called Bravais Lattices.

`text(Seven crystal systems)` : The seven crystal systems are given in fig.