Earth Science Metamorphic rock

Objectives: Describe two ways a rock can undergo metamorphism. Explain how the mineral composition of rocks changes as the rocks undergo metamorphism. Describe the difference between foliated and non-foliated metamorphic rock.

Origins of Metamorphic Rock Metamorphic rocks 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 or pressure of the new environment is different from the one in which the rock formed the rock will undergo metamorphism

Regional metamorphism Contact metamorphism When magma moves through the crust, the magma heats the surrounding rock and changes it. 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 curst collide with each other.

Composition of Metamorphic Rock As rocks undergo metamorphism Original minerals in a rock change into new minerals that are more stable in the new pressure and temperature conditions. Index minerals (form only in metamorphic rock) Are used to estimate Temperature Depth Pressure ---- at which a rock undergoes metamorphism. calcite + + + Heat and Pressure = quartz hematite Garnet

Texture of Metamorphic Rock Two types: Foliated Metamorphic Rock Mineral grains are arranged in planes or band Nonfoliated Metamorphic Rock Mineral grains are not arranged in planes or band commonly made of one or only a few minerals.

This shows what happens to shale, a sedimentary rock, when it is exposed to more and more heat and pressure. Slate Shale Phylite Gneiss Schist

Two examples of nonfoliated metamorphic rock undergoes metamorphism limestone Marble undergoes metamorphism Sandstone Quartzite

Metamorphic Rock Structures Metamorphic rock has features that indicates its history. These features are caused by deformation: Change in the shape of a rock caused by a force placed on it. These forces may cause a rock to be squeezed or stretched.