Metamorphic rocks are created when existing igneous or sedimentary rocks are squashed, stretched and/or cooked and change their appearance and mineral composition.
Some metamorphic rocks have course-grained minerals that occur in wavy bands. Others are very fine-grained. Most are hard and difficult to break.
Kavanaugh, Pocket Naturalist
- Kavanaugh, James. Pocket Naturalist - Geology - An Introduction to familiar Rocks, Minerals, Gemstones & Fossils, Waterford Press: Arizona (2000)