Metamorphic Rock Forms
Metamorphic rocks are formed from sedimentary or igneous rocks with physical or chemical
alterations caused by heat, pressure, or the infiltration of other materials. Metamorphic rocks can
be classified as either foliated or nonfoliated; foliation refers to the rock flaking or splitting into
thin slabs. The types of foliated and nonfoliated metamorphic rocks and their mineral
compositions follow the felsic-mafic distinctions including feldspar-silica minerals (felsic) and
magnesium-ferric minerals (mafic). Many of the rocks may appear to have the same
mineralogical composition, but they differ in their crystalline structure and particle size.
Identification and minerals analysis is best made by field investigation.
 Foliated Metamorphic Rocks- The foliated metamorphic rocks include slate, phyllite,
schist, gneiss, and their mafic equivalents. The rock types grade from slate to gneiss
according to low and high degrees of metamorphism.
 Nonfoliated Metamorphic Rocks- The nonfoliated metamorphic rocks include hornfels,
quartzite, and marble. These usually occur in small, scattered deposits. Quartzite is the
most common.
Distribution
Metamorphic rocks are scattered over the surface of the earth occurring especially in
mountainous regions.
 North America, United States and Canada- Most of the major mountainous areas of the
United States contain metamorphic rock. The Appalachian Mountains from New England
to Georgia contain metamorphic rocks, including prominent formations of slate, gneiss,
and schist. The Rocky Mountains contain many of these rocks, as does the Alaskan
Range. Smaller scattered deposits are found in Texas, Minnesota, and the Dakotas.
Metamorphic rock forms are found in the Canadian Rockies, southeastern Canada, and
New Brunswick.
 South and Central America- Principal metamorphic forms are found along the Andes
Mountain chain from Columbia through Chile. Others are located in eastern Brazil,
northeastern Venezuela, and northern Guyana. Central America has small, scattered
forms in southern Mexico and through the mountainous regions of Guatemala.
 Africa- Complex mixtures of metamorphic rocks and associated igneous rock structures
occur throughout Africa. Major forms are found throughout the Near East, in the United
Arab Republic, and in Saudi Arabia.
 Europe- Metamorphic rocks are found in the Urals and the Alps, and in Sweden, Finland,
and Norway.
 Asia- Mixed, complex rock structures and ancient metamorphic and associated igneous
rock structures occur together throughout Asia. Metamorphic rocks are not found in all of
the areas; where there may be only small areas.
 Australia- Major metamorphic deposits are found in the northern regions, but scattered
forms exist throughout the entire region.
 Pacific and Caribbean Regions- Significant forms are not found in the Pacific Islands
region.
 Small, scattered deposits can be found throughout the Caribbean region, including Cuba,
Puerto Rico, and the West Indies.
Source: Terrain analysis procedural guide for surface configuration, US Army engineer
topographic laboratories, 7-119