sentence: Slate is a metamorphic rock that is a useful building material.
sentences_before: Metamorphic rock is rock that has been changed. Sometimes an igneous, or a sedimentary rock can be heated, or squashed under the ground, so that it changes. Metamorphic rock is often harder than the rock that it was before it changed. One well-known metamorphic rock is marble which is valued for its different colours, and because it can be carved and polished.
concept_name: slate
headings: Geology Types of rock Metamorphic rock