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Northern Ireland Geology - Granite

Granite is an igneous rock which has cooled slowly. The crystals are clearly visible with the naked eye. Most granites have three minerals which can be easily distinguished. Quartz is a clear or greyish 'glassy' mineral. Mica is a soft black mineral which splits into thin flakes. The third mineral, feldspar, occurs in a range of colours. Pink or white feldspar is known as orthoclase while the other colour that occurs, grey, is known as plagioclase.

The Slieve Gullion area of south County Down has a very complex geology. Much clearer are the granite outcrops in the Mourne Mountains. They make up about 150 square kilometres of south east County Down. In places a 'roof' of sediment can be seen indicating that the Mourne granites were intruded into Silurian shales and greywaches. This intrusion did not reach the surface and the molten rock cooled very slowly allowing large crystals to grow.

The granites of the Mournes are associated with the volcanic activity in the Tertiary Period, some 60 Million years ago.

Granite data Granite sample

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