How will you justify that stone is more rigid than iron?
We know that the rigid property can be characterized by the modulus of rigidity (shearing modulus) which is the ratio of shear stress to shear strain, i.e.
Shear modulus = Shear stress / shear strain
For same shear stress, shear strain in the iron is more than that of in stone, i.e. stone offers more resistance to the deforming force than iron. Hence, stone is more rigid than iron.