Download Metamorphic rocks|A1 Sample answer

Metamorphic rocks| A1 Sample answer
Explain the formation of metamorphic rocks with reference
to examples from Ireland. (2013 Q1B)
Metamorphic rocks are formed when the appearance, texture and chemical composition of igneous or
sedimentary rocks are changed by great heat, pressure or a combination of the two. Great heat from magma
or grate pressure as a result of tectonic activity such as folding can cause igneous or sedimentary rocks to
change into metamorphic rocks. Marble and quartzite are both metamorphic rocks found in Ireland.
Metamorphism is the changing into a metamorphic rock. There are two types of metamorphism, regional
metamorphism and thermal metamorphism. Thermal occurs due to heat alone. The rocks are exposed to the
heat of the earth’s magma and as a result their make-up changes. Regional metamorphism happens due to
great heat and pressure over a large area over a large period of time. This usually happens when foldmountains are formed. Great heat and pressure affects the rocks as the plates converge and the magma
underneath them rises. This happened during the Caledonian fold mountain building period in Ireland.
Due to regional metamorphism, limestone changes into marble. Marble is a hard crystalline rock of various
colours. It is found in Connemara, Co. Galway; Cork; and Rathlin Island in Antrim. White marble is the
purest form and it is a result of pure limestone changing form. However when impurities exist such as iron
oxides, silt, sand and clay, marble will look discoloured. For example, famous Connemara marble is green
and Cork marble is red.
Sandston changes into quartzite. It is changed due to great heat and pressure also. Ireland’s sandstone can be
found in the Sugarloaf, Co. Wicklow and in Croagh Patrick, Mayo. During Caledonian mountain building,
sandstone came into contact with magma. Since there were spaces between the grains of quartz in the rock,
these were filled up with silica and both were packed together. Quartzite is a lightly coloured rock and often
is white. It is usually found at the peak of mountains.
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Metamorphic rocks | Sample answer