Question

What is the cleavage property of solids? And why crystalline solids on being cut generate plain surfaces?

Answer 1

The cleavage property is shown by crystalline solids because they possess cleavage planes. In a crystalline solid, the cells are neatly stacked. The cleavage planes are areas where the crystal structure is the weakest. It is only along these planes that a crystalline solid can be cut. Therefore, a cut from a sharp object would give two smooth parts. Amorphous solids do not show any cleavage planes.

If you look at the crystal structure, you will notice a constant arrangement of the unit cells. In the two-dimensional diagram, it is seen as a lattice. Usually, the cuts made in the direction of the linear sequence of points are preferred over other cuts. In other words, the cuts that preserve the arrangement of the particles are preferred in a crystalline solid.

An example is of the diamond, a crystalline solid that when cut along the cleavage planes gives small diamonds with smooth edges having the same arrangement of the particles as that of the parent diamond.