The hardness of ferro silicon is due to its high silicon content, which can range from 15% to 90%. The silicon atoms bond strongly with the iron atoms, creating a rigid and compact crystal structure that offers excellent resistance to wear and tear.

Because of its high hardness, ferro silicon is widely used in the production of abrasives, cutting tools, and other wear-resistant materials. It is also a popular additive in steel making, where it helps to increase the strength and hardness of the finished products.