Stretching from Carrickfergus in County Antrim to the City of Derry Airport in County Londonderry, the Causeway Coast and Glens area includes some of the most geologically diverse landscapes on Earth with dramatic coastline sculpted by millions of years of geological activity, weathering and erosion. In particular, the rich geology and biodiversity along the coastline of Islandmagee combines with coastal processes at the Gobbins to present a landscape of exceptional scientific, aesthetic, historical and cultural value.
The Gobbins Cliffs
The Gobbins Cliff Path winds around almost vertical basalt sea cliffs up to 60m (196ft) in height.
Basalt is a common extrusive igneous rock with a fine crystal structure. It usually forms when lava cools relatively quickly at the Earth's surface. Where magma (lava which hasn't reached the surface) cools more slowly within the Earth's crust, it tends to produce rocks with coarser crystals e.g. Dolerite and Gabbro. The chemical composition of these rocks is quite similar to basalt; however the slower cooling allows larger crystals to develop and gives the rocks a different appearance.
The basalts which give rise to the dramatic cliffs on the East Coast of Islandmagee are relatively common in north Antrim. They formed as part of a series of huge fissure eruptions which created the impressive Antrim Plateau, extending from Cave Hill outside Belfast to Binevenagh Mountain in the north-west of County Londonderry. Fissure eruptions basically mean that as North America and Europe began to drift apart approximately 60 million years ago, large cracks opened in the Earth's surface, and through these cracks lava flooded onto the surface.
Near the Gobbins there is evidence of the type of landscape which existed before these basalt rocks came to dominate. At the south end of the site, older marine sedimentary rocks are visible. These rocks are some 200 million years old and provide us with evidence for the climate and landscape during the late Triassic and early Jurassic Periods, when this part of Ireland would have been located under a warm shallow sea. The impressive ichthyosaur fossil found at Waterloo Beds in Larne dates from this period.
Overlying the older marine sediments, is younger cretaceous limestone. These rocks formed between 144 and 65 million years ago when this part of Ireland was located under a warm shallow "chalk sea", rich in marine life, which upon death formed thick deposits of calcite from the bones and shells of marine animals. Exposures of this limestone can be seen to the south of the site and in the vicinity of Portmuck Bay. The same limestone can be seen along the Antrim Coast Road between Larne and Carnlough.
Hill's Port Basalt / Gobbinsite
Whilst the basalt which overlays the cretaceous white limestone at the Gobbins is abundant across County Antrim, the basalt at Hill's Port is quite special. It is what is known as amygdaloidal basalt.
When lava cools, gases are trapped forming small bubbles within the rock. If there is sufficient gas this can create significant numbers of relatively large bubbles or vesicles within basalt rock. This is particularly common at the top of a lava flow because gas bubbles will always rise. Over time the small vesicles are filled with minerals precipitated from fluids within the rock. At The Gobbins the vesicles in the basalt have been filled with an impressive array of silica based minerals, one of which - Gobbinsite - is named after the location in which it was first discovered! None of the minerals are economically valuable; however they do give rise to the speckled appearance of the basalt along the cliff path.
Examples of minerals found in amygdaloidal basalt at the Gobbins include:
Gobbinsite - named after the Gobbins, where it was first recorded as a new mineral in 1982. This mineral is also recorded at the Giant's Causeway and in Mont Saint-Hilaire, Canada. Gobbinsite is chalky white to brown in colour and similar in hardness to steel.
Gmelinite - an uncommon mineral first recorded by David Brewster from the University of Tubingen, Germany in 1825. Gmelinite is known to occur at the Gobbins and Little Deer Park Quarry in Glenarm. Outside Northern Ireland it is recorded in Italy, Kazakhstan, Australia and the USA. Gmelinite is orange to pink in colour and similar in hardness to steel.
Analcime - occurs frequently in basalt. It is usually white or colourless and similar in hardness to cobalt.
Chabazite - a common mineral, very closely related to gmelinite. It is peach or white in colour and similar in hardness to steel.
Cowlesite - a rare mineral, first recorded in Oregon, USA in 1975. It is known to occur in the USA, Canada, Russia and Iceland. It is colourless or white and similar in hardness to calcium.
Gonnardite - a relatively common mineral, first recorded in France in 1896. It is known to occur at sites across the globe. Gonnardite is white in colour and similar in hardness to the enamel on your teeth.
Heulandite - a common mineral, known to occur across the globe. It is white to beige in colour and similar in hardness to platinum.
Levyne - an uncommon mineral, only found in cavities within basalt. It was first recorded in rocks from the Faroe Islands but is known to occur at sites across the globe. It is colourless or white and similar in hardness to iron.
Mesolite - a relatively uncommon, white or colourless needle like mineral found across the globe. It is similar in hardness to volcanic glass (obsidian). Spectacular needle sprays are found in Skookumchuck Dam, Washington State, USA.