M ETAMORPHIC R OCKS c. Classify rocks by their process of formation. d. Describe processes that change rocks and the surface of the earth.

M ETAMORPHIC R OCK  “ Meta ” is ancient Greek for change.  “ Morphosis ” is ancient Greek for form.  Metamorphic rock then is rock that has changed from one form to another.

O RIGINS OF M ETAMORPHIC R OCK  Metamorphic rocks are rocks in which the structure, texture, or composition of the rock have changed. All three types of rock can be changed by heat, pressure, or a combination of both.  A rock’s texture or mineral composition can change when its surroundings change. If the temperature of pressure of the new environment is different from the one in which the rock formed, the rock will undergo metamorphism.

C ONTACT M ETAMORPHISM  Contact Metamorphism when magma moves through the crust, the magma heats the surrounding rock and changes it.  Some minerals in the surrounding rock are changed into other minerals by this increase in temperature.  The greatest change occurs where magma comes into direct contact with the surrounding rock.

R EGIONAL M ETAMORPHISM  Regional metamorphism occurs when pressure builds up in rock that is buried deep below other rock formations, or when large pieces of the Earth’s crust collide with each other.  The increased pressure and temperature causes rock to become deformed and chemically changed.

M ETAMORPHISM

H OW M ETAMORPHIC R OCKS F ORM  Deep below the Earth’s surface the intense heat and pressure can change rocks.  Their appearance, texture, crystal structure and mineral content can change.  Fossils will be destroyed.

A LMOST M ELTED !  Metamorphic rocks are often squished, smeared out, and folded.  Despite these uncomfortable conditions, metamorphic rocks do not get hot enough to melt, or they would become igneous rocks.

C LASSIFYING  Classified by the arrangement of the grains.  Foliated  Non-foliated  Usually harder and denser than the rock they come from.

T EXTURE OF M ETAMORPHIC R OCK  All metamorphic rock has one of two textures.  Foliated Metamorphic Rock  Non-foliated Metamorphic Rock

F OLIATED M ETAMORPHIC R OCK  Grains are in parallel layers of bands.  “Foliated” is the Latin word for leaf.  Describes the thin layering found in many metamorphic rocks.  These rocks will split these bands.

S LATE  Formed when shale is subjected to pressure.  Denser, more compacted than shale.  Produces flat plates when broken.

S LATE TO S CHIST  If slate is subjected to even greater pressure and moderate temperatures, schist is formed.

G RANITE TO G NEISS Granite becomes gneiss when subjected to heat and pressure.

K EY I DEA !  Heat + Pressure = metamorphic rock

N ON -F OLIATED R OCK  Mineral grains are randomized.  Amorphous  Do not split into layers  Usually smoother and denser than the parent rock.

Q UARTZITE  Occurs when sandstone is compressed by pressure.  Usually very hard.

M ARBLE  Formed from metamorphosed limestone  Much harder and denser