Essay - Metamorphic rocks formation

Q. Discuss the formation of metamorphic rocks

• Metamorphic rocks were once either igneous or sedimentary but were transformed both physically and chemically under great heat and/or pressure

• Three types of metamorphism

1. Thermal/contact

• When rocks are formed as a result of intense heat alone

• Occurs in areas of volcanic activity

• The magma or lava almost cooks the rocks it comes into contact with

• Rocks formed this way are known as aureoles

2. Regional

• When rocks are transformed as a result of both intense heat and high pressure

• Occurs during folding as a result of the pressure of colliding plates

3. Dynamic

• When rocks are transformed as a result of high pressure alone

• Occurs when pieces of crust slip past each other in opposite directions causing deformation

• Rocks and their parent rocks

1. Marble

• Coarse grained and crystalline rock

• Originally limestone

• Pure marble is white. Different chemical compositions give variations in colour (e.g. iron oxide gives red tinge, serpentine gives green tinge)

• Used mainly for ornamental purposes e.g. worktops an fireplaces

• Formed through thermal/contact metamorphism (plates collide and limestone is subducted. Upon entering the mantle, magma rises and surrounds the limestone, changing it to marble)

2. Quartzite

• Hard, non-porous and erosion-resistant white or grey rock

• Originally sandstone

• It was crystallised after the spaces between the sand grains were filled with silica

• Used mainly for road surfacing

• Can be found at the summit of the Sugar Loaf

• Formed through regional metamorphism

3. Slate

• Fine-grained, dark grey or black rock

• Originally shale

• Splits easily into thin layers (so is used for roofing)

• Can be found in Valentia (Co. Kerry)

• Formed through dynamic metamorphism (Shale is put under immense pressure from destructive/convergent plates. The pressure compresses the shale into strata, forming slate)