If steel (a metal) is hard and gran

If steel (a metal) is hard and granite (a nonmetal) is hard, why don’t we make automobile engines out of granite?
Although the property of “hardness” is similar for steel and granite, other properties aren’t as desirable for manufacturing automobile engines. For example, the low heat conduction of rocks make them explode under high temperature. They are also brittle, making them poor for use in engine blocks.