Carneal ASSI

The Carneal area is a special place because of its earth science interest. The area provides access to an unusual rock series related to a volcanic intrusion within the areas chalk rocks.

Some 60 million years ago, when much of north-east Ireland was experiencing extensive eruptions of basalt lavas, a vertical plug of dolerite was injected into the chalk and overlying basalt.

Volcanic plugs were the main feeder tubes to surface volcanoes now blocked with solidified magma. The passage of molten rock, at temperatures around 1100-1200ºC, heats the wall rocks to very high temperatures and changes them by the process of thermal metamorphism.

The volcanic neck at Carneal passes through Ulster White Limestone and, when in the molten state, the ascending lava reacted chemically and physically with the limestone to create an uncommon series of minerals called calc-silicates that can now be seen here.

The chalk has been metamorphosed by heat to form marble. The margins of the chalk were altered through exchange of minerals between the chalk and molten dolerite while the dolerite was altered through mixing with the chalk.

Carneal is one of a small number of important mineralogical sites where evidence of these processes can be found. These sites have shown how, on a small-scale, unusual minerals can be generated by mixing and interaction between different rock types.