21. Cleavage in a mineral results from three dimensional silicate structure b. external crystal faces c. Silica tetrahedra d. planes of weak bonding between certain layers of atoms e. the higher numbers on Moh's Scale

d. planes of weak bonding between certain layers of atoms

Explanation:

Cleavage, is a type of planar feature of the rock, which develops due to the metamorphism and deformation.

It is a secondary type of rock foliation, i. e., the separation between two rocks.

They are formed in fine grained rocks which is made from minerals, under high pressure.

The weak bonding between layers of atom, generates a cleavage.