Rocks

Rocks are composed of assemblages of minerals. They are classified into three primary categories: igneous, sedimentary and metamorphic. Igneous rocks form from magmas and lavas, sedimentary rocks are formed due to the erosion of existing rocks at the Earth’s surface, and metamorphic rocks are formed by alteration of existing rocks under high temperature and pressure conditions in the Earth’s crust.

This geological map of Ireland (from the Geological Survey of Ireland) shows representatives of all three types, from the sedimentary ‘Old Red’ Sandstone in the south (pale orange), and Carboniferous limestone across the midlands (pale blue), to the igneous Antrim basalts (pale purple) and the Leinster, Galway and Donegal granites (bright red), and finally the metamorphic schists and gneisses of Donegal and Mayo (pale pink).