Metamorphic rocks have been modified by heat, pressure, and chemical processes, usually while buried deep below Earth’s surface. Exposure to these extreme conditions has altered the mineralogy, texture, and chemical composition of the rocks.

There are two basic types of metamorphic rocks. Foliated metamorphic rocks have a layered or banded appearance that is produced by exposure to heat and directed pressure. Examples of foliated rocks include: gneiss, phyllite, schist, and slate

Non-foliated metamorphic rocks do not have a layered or banded appearance. Examples of nonfoliated rocks include: hornfels, marble, novaculite, quartzite, and skarn.