Metamorphic RocksGneiss

Metamorphic rocks are: the result of the application of heat, pressure and directed stress, or some combination of these effects applied to pre-existing rock of any type.

The process by which metamorphic rocks are produced is called metamorphism. Slate

Metamorphic Rocks

2 TYPES OF TEXTURES – FOLIATEDAND NON-FOLIATED

Foliated = banded rock, minerals are arranged in bands, or thin sheets/layers

Non-foliated = unbanded rock, usually consist of all one type of mineral so may appear to have a granular or uniform texture

Ex.) quartz (sand grains) makes up quartzite, calcite (limestone) makes up marble

Foliated –vs- Non-foliated Metamorphic Textures

Foliated – looking at thin section under microscope

Non-foliated – looking at thin section under microscope

Foliated Texture

Forms when minerals (many of which are platy micas such as biotite and muscovite) line up producing a

distinct layering in the rock.

Minerals tend to line up perpendicular to the pressure

Foliated Texture

Foliated Texture

The layering of minerals produces three distinctly different looking rocks, those with slaty cleavage (e.g. slate), schistosity (e.g. schist), and mineral banding (or gneiss texture).

Changes undergone to rocks during metamorphism

Slaty Cleavage Foliation

Slate

Phyllite

Phyllite

Schistosity Foliation

Schist

Mica Schist

Garnet Schist

Banding in Foliation

Gneiss

TYPES OF METAMORPHISM:

REGIONAL – large scale metamorphism (over large areas , up to thousands of square feet) – think mountains

LOCAL – smaller scale metamorphism

Contact – think burn on

your finger

Deformational/Dynamic –think bent finger – smashedin the door

Types of Metamorphism

Regional Metamorphism

Occurs during mountain building

On a large scale (over large areas)

Forms most of the metamorphic rocks of Earth’s crust

Rocks are subject to high heat and high pressure

The result is a rock that has pronounced foliation and layering.(The foliation is usually perpendicular to the direction of the applied stress.)

T, P ( )

Local Metamorphism –

Contact

Occurs on a smaller scale

when hot magma (liquid and gases) move into the parent/country rock, heating and changing it. (so

its close to magma)

Usually non-foliated and appear to have a sugary texture

( T)

Local Metamorphism –Deformational/Dynamic

Occurs on a smaller scale

in fault zones (so friction & pressure change the rock)

Can have sugary texture (non-foliated) or be foliated

( T, P)

Examples of Metamorphic Rocks

Quartzite – parent rock is Sandstone

Examples of Metamorphic Rocks

Marble – parent rock is Limestone

Examples of Metamorphic Rocks

Slate – parent rock is Shale

Examples of Metamorphic Rocks

Phyllite – parent rock is Shale

Examples of Metamorphic Rocks

Schist – parent rock is Shale (sometimes granite or other rocks, depending on the content)

Mica Schist

Garnet Schist

Examples of Metamorphic Rocks

Gneiss – parent rock is Shale, Granite, or conglomerate (sometimes other rocks, depending on the content)

(Metamorphic Website)