A dolerite, also called a diabase, is an igneous rock, which means it was generated from the cooling and solidification of molten Earth material. It is also referred to as a volcanic rock.
The dolerite rock is similar to basalt, but it is coarser in texture and contains crystals that can be viewed with a hand-held lens because dolerite cools more slowly than basalt. Several dolerites are present in Ireland. The most famous is the dolerite plug at Slemish. Others include Corkey Rocks, Sandy Braes, Tievebulliagh and the columns at Ballygalley Head. Dolerite rocks are also found in dikes and sills.