Why are metamorphic rocks usually harder and denser than their parent rocks?

Explanation:

Metamorphic rocks are harder and denser than their parent rocks because they started off the same as their parent rocks but at some point were met with extreme heat and pressure. These conditions melted and compressed the parent rocks so much that it created metamorphic rock that was extremely hard and dense. This is why metamorphic rocks are usually found deep under the Earth's surface.