Question

Many of the hardest rocks are metamorphic rocks. Why do you think metamorphic rocks are harder than sedimentary rocks?

Answer 1

Answer:

Metamorphic rocks are almost always harder than sedimentary rocks. They are generally as hard and sometimes harder than igneous rocks. They form the roots of many mountain chains and are exposed to the surface after the softer outer layers of rocks are eroded away.  

Because their mineral grains grew together tightly during metamorphism, they're generally strong rocks.