GEOL 1601 Chapter : What Are Metamorphic Rocks
Document Summary
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 such as gneiss, phyllite, schist, and slate have a layered or banded appearance that is produced by exposure to heat and directed pressure. Non-foliated metamorphic rocks such as hornfels, marble, quartzite, and novaculite do not have a layered or banded appearance. Pictures and brief descriptions of some common types of metamorphic rocks are shown on this page. Hornfels is a fine-grained nonfoliated metamorphic rock with no specific composition. Hornfels is a rock that was "baked" while near a heat source such as a magma chamber, sill, or dike. Gneiss is a foliated metamorphic rock that has a banded appearance and is made up of granular mineral grains. It typically contains abundant quartz or feldspar minerals.
