Metamorphic Rocks A metamorphic rock is a pre-existing rock that has changed due to its exposure totremendous heat, pressure and/or mineral fluids.
Formation of Metamorphic Rocks Metamorphism – or the process of making metamorphic rock – takes place within the lithosphere. ContactMetamorphism – The metamorphism of rock that comes into contact with igneous intrusions and/or extrusions. RegionalMetamorphism – The metamorphism of rock that is associated with motions of the Earth’s lithosphere.
ContactMetamorphism 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. ContactMetamorphism 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.
RegionalMetamorphism RegionalMetamorphism will occur in rock that is subjected to the intense heat and pressure created by movement within the Earth’s lithosphere. 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.
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. GNEISS: coarse-grained crystals SLATE: fine-grained crystals SCHIST: medium-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 NonfoliatedMetamorphic Rock Nonfoliatedmetamorphic rocks do notcontainlayers of minerals. Minerals within these rocks are interconnecteddue to exposure to high heatbut not as highpressure.Nonfoliatedrocks are associated withcontact and/or regional metamorphism. Bands are NOT present in nonfoliated metamorphic rock. Nonfoliatedmetamorphic rocks can be made up ofone 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?” “Which foliated, metamorphic rock is medium grained and contains platy mica crystals?” SCHIST MARBLE