Metamorphic Rocks

A metamorphic rock is a pre-existing rock that has changed due to its exposure to tremendous heat, pressure and/or mineral fluids.

Formation of Metamorphic Rocks

Metamorphism – or the process of making metamorphic rock – takes

place within the lithosphere.

Contact Metamorphism – The

metamorphism of rock that comes into

contact with igneous intrusions and/or

extrusions.

Regional Metamorphism – The metamorphism of rock that is associated with motions of the Earth’s lithosphere.

Contact Metamorphism

Contact Metamorphism will occur in rock that is adjacent to an igneous intrusion or

extrusion.

The rock that the magma or lava flows across will be changed due to an increase in temperature and its reactions with

the liquified minerals in the magma/lava. Zone of contact metamorphism

A gabbro (igneous) intrusion can be seen above (black-colored rock). The surrounding gray rock is limestone. A thin layer of marble (white-colored rock) can be found between

the two types of rocks. The marble formed as a result of contact metamorphism.

Regional Metamorphism

The Himalayan Mountains were created through motions within the Earth’s lithosphere. These motions created a great deal of heat and pressure in the rock transforming the rock through

regional metamorphism.

Regional Metamorphism will occur in rock that is

subjected to the intense heat and pressure

created by movement within the Earth’s

lithosphere.

Types of Metamorphic Rocks

Foliated Metamorphic Rock

Foliated metamorphic rock contains layers of minerals that have recrystallized due to exposure to high heat and high pressure.

Foliated rocks are associated with regional metamorphism.

These layers of recrystallized minerals can be seen as bands.

Most foliated metamorphic rocks are made up of several minerals.

SLATE: fine-grained crystals SCHIST: medium-grained crystals GNEISS: coarse-grained crystals

The more heat and pressure associated with regional metamorphism, the more minerals will recrystallize and realign into bands within a metamorphic rock.

Types of Metamorphic Rocks

Nonfoliated Metamorphic Rock

Nonfoliated metamorphic rocks do not contain layers of minerals. Minerals within these rocks are interconnected due to exposure to high heat but not

as high pressure. Nonfoliated rocks are associated with contact and/or regional metamorphism.

Bands are NOT present in nonfoliated metamorphic rock.

Nonfoliated metamorphic rocks can be made up of one mineral or several minerals.

The high heat and pressure have caused the pebbles in this METACONGLOMERATE to

“stretch”.

The QUARTZITE and MARBLE lack bands associated with foliated rocks. Both metamorphic rocks formed from one mineral (quartz) or a

monomineralic rock (limestone).

Identification of Metamorphic Rocks RT = Pg. 7

“Which metamorphic rock would react with hydrochloric acid?” MARBLE

“Which foliated, metamorphic rock is medium grained and

contains platy mica crystals?”SCHIST