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Rock Types

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The three main types of rocks - Igneous, Sedimentary, and Metamorphic - are all represented on Arran. Follow the links on this page to find out more about the representatives of each type that you will be able to see on Arran.


Sedimentary rocks are formed from sediments derived from existing rocks during erosion - for example by rivers or wind - or from organic origin (eg. coal) or precipitation (some limestones). The process that transforms unconsolidated sediments into rock is known as diagenesis.



Igneous rocks crystallise from molten magma - either slowly beneath the surface of the Earth (e.g. granite), or more quickly at the surface after being erupted from a volcano or along narrow dykes or sills (e.g. basalt).



Metamorphic rocks, the third major category, are those which have been formed by the alteration of existing rocks due to heat, pressure or percolating fluids.

University of Glasgow