Scawt Hill

Last updated
Scawt Hill
The Sallagh Road near Cairncastle - - 324141.jpg
Scawt Hill from the Sallagh Road, Cairncastle
Highest point
Elevation 378 m (1,240 ft)
Coordinates 54°54′38″N5°54′55″W / 54.9105°N 5.9154°W / 54.9105; -5.9154 Coordinates: 54°54′38″N5°54′55″W / 54.9105°N 5.9154°W / 54.9105; -5.9154
Relief Map of Northern Ireland.png
Red triangle with thick white border.svg
Location in Northern Ireland
Location County Antrim, Northern Ireland
OSI/OSNI grid D338090
Topo map OSNI Discoverer 9
Mountain type Volcanic plug

Scawt Hill is a volcanic plug in County Antrim, Northern Ireland, in the borough of Larne, 5 km from the village of Ballygally. [1]


It gets its name from the Ulster Scots 'scawd' meaning scaly, scabby or rugged. [2] Alternatively, 'scawt' meaning scruffy and contemptible, and when applied to rocks, covered in barnacles. [3]

Discovery of minerals

Scawt Hill is notable for being the type locality for several hydrated calcium silicates, [4] that is, the place where they were first identified. These minerals were formed when the existing chalk of the area was intensely altered by the intrusion of the feeder tube of an ancient volcano, now long since cooled and eroded to its roots. [5]

Minerals that were first discovered at Scawt Hill:

In all, 28 minerals have been found at this site. [11]

Volcanic plugs in Northern Ireland

Over 30 volcanic plugs are dotted through Northern Ireland, mostly along the Antrim coast like Scawt Hill, although they are relatively rare throughout the rest of Ireland. Volcanic plugs are often easy to spot. Their harder rock erodes away more slowly than their surroundings so they rise above the landscape as a hill. [5]

The largest volcanic plug in Northern Ireland is the oval-shaped Slemish. At its widest, Slemish is over 1 km in diameter. [5] Scawt Hill is more of a typically sized example. This olivine dolerite plug is 270 m x 180 m wide and rises 30 – 60 m above the Cretaceous white limestone (chalk), although the Antrim plateau around it is typically basalt. [1]

At Scawt Hill, Cretaceous chalk, the white rock to the left of the photo, has been intruded by molten rock which cooled to dolerite, the darker rock to the right Scawt Hill - - 454783.jpg
At Scawt Hill, Cretaceous chalk, the white rock to the left of the photo, has been intruded by molten rock which cooled to dolerite, the darker rock to the right
Scawt Hill from Ballygally Ballygally - - 428626.jpg
Scawt Hill from Ballygally

Due to the volcanic intrusion the chalk around Scawt Hill has been transformed by high temperature and low pressure thermal metamorphism, developing the large and unusual range of calc-siliate minerals that have attracted interest. The rocks inside the vent were also changed by the contact, producing a sequence of alkali mafic igneous rocks as the magma assimilated the chalk, reducing the silica in the magma and leading to larger grain size near the contact. [1]

Early description of Scawt Hill

Cecil Edgar Tilley, writing for the Mineralogical Magazine in 1929, was the first to appreciate the potential of the dolerite-limestone contact at Scawt Hill. Tilley named scawtite and larnite, and later, rankinite, and his writings inspired many others to find similar relationships between rocks worldwide. [1]

Protected status

In 1995, Scawt Hill was categorised as an Area of Special Scientific Interest, not just for its international importance to geology, but for its plant life, where chalky and alkaline conditions are in close proximity, and for its conditions for breeding birds. [12]

Ulster Way

Scawt Hill is on the Ulster Way, part of a series of walking routes which encircle Ulster. It is passed by between the Black Hill and the Sallagh Braes. [13]

See also

Geology of Northern Ireland
Volcanic plugs of Northern Ireland

Related Research Articles

Larne Town (and civil parish) in County Antrim, Northern Ireland

Larne from Irish: Latharna, the name of a Gaelic territory) Scots: Lairne is a seaport and industrial market town, as well as a civil parish, on the east coast of County Antrim, Northern Ireland, with a population of 18,755 people at the 2011 Census. The Larne Local Government District had a population of 32,180 in 2011. It has been used as a seaport for over 1,000 years, and is today a major passenger and freight roll-on roll-off port. Larne is administered by Mid and East Antrim Borough Council. Together with parts of the neighbouring districts of Antrim and Newtownabbey and Causeway Coast and Glens, it forms the East Antrim constituency for elections to the Westminster Parliament and Northern Ireland Assembly. The civil parish is situated in the historic barony of Glenarm Upper.

Diabase An intrusive mafic rock forming dykes or sills

Diabase or dolerite or microgabbro is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine grained to aphanitic chilled margins which may contain tachylite. Diabase is the preferred name in North America, while dolerite is the preferred name in the rest of English-speaking world, where sometimes the name diabase is applied to altered dolerites and basalts. Some geologists prefer the name microgabbro to avoid this confusion.

Volcanic plug Volcanic object created when magma hardens within a vent on an active volcano

A volcanic plug, also called a volcanic neck or lava neck, is a volcanic object created when magma hardens within a vent on an active volcano. When present, a plug can cause an extreme build-up of pressure if rising volatile-charged magma is trapped beneath it, and this can sometimes lead to an explosive eruption. Glacial erosion can lead to exposure of the plug on one side, while a long slope of material remains on the opposite side. Such landforms are called crag and tail. If a plug is preserved, erosion may remove the surrounding rock while the erosion-resistant plug remains, producing a distinctive upstanding landform.

Whitehead, County Antrim Human settlement in Northern Ireland

Whitehead is a small seaside town on the east coast of County Antrim, Northern Ireland, lying almost midway between the towns of Carrickfergus and Larne. It lies within the civil parish of Templecorran, the historic barony of Belfast Lower, and is part of Mid and East Antrim Borough Council. Before the Plantation of Ulster its name was recorded as both Whitehead and Kinbaine.

Slemish Mountain in Antrim, N. Ireland

Slemish, historically called Slieve Mish, is a small mountain in County Antrim, Northern Ireland. It lies a few miles east of Ballymena, in the townland of Carnstroan. Tradition holds that Saint Patrick, enslaved as a youth, was brought to this area and tended sheep herds on Slemish, and that during this time he found God.

Ballygally Irish village

Ballygally or Ballygalley is a village and holiday resort in County Antrim, Northern Ireland which lies on the Antrim coast, approximately 3 miles north of Larne. It is also a townland of 769 acres and is situated in the civil parish of Carncastle and the historic barony of Glenarm Upper. It had a population of 821 in the 2011 Census. It is located within the Mid and East Antrim Borough Council area.

Larimar blue gemstone from the Dominican Republic

Larimar, also called "Stefilia's Stone", is a rare blue variety of the silicate mineral pectolite found only in the Dominican Republic, in the Caribbean. Its coloration varies from white, light-blue, green-blue to deep blue.

Brownmillerite oxide mineral

Brownmillerite is a rare oxide mineral with chemical formula Ca2(Al,Fe)2O5. It is named for Lorrin Thomas Brownmiller (1902–1990), chief chemist of the Alpha Portland Cement Company, Easton, Pennsylvania.

Carrick-a-Rede Rope Bridge rope bridge near Ballintoy, Antrim, Northern Ireland

The Carrick-a-Rede Rope Bridge is a rope bridge near Ballintoy in County Antrim, Northern Ireland. The bridge links the mainland to the tiny island of Carrickarede. It spans 20 metres (66 ft) and is 30 metres (98 ft) above the rocks below. The bridge is mainly a tourist attraction and is owned and maintained by the National Trust. In 2018, the bridge had 491,947 visitors. The bridge is open all year round and people may cross it for a fee.

Type locality, also called type area, or type section, is the locality where a particular rock type, stratigraphic unit or mineral species is first identified. If the stratigraphic unit in a locality is layered, it is called a stratotype, whereas the standard of reference for unlayered rocks is the type locality.

Prof Cecil Edgar Tilley FRS HFRSE PGS was an Australian-British petrologist and geologist.

Ettringite sulfate mineral

Ettringite is a hydrous calcium aluminium sulfate mineral with formula: Ca6Al2(SO4)3(OH)12·26H2O. It is a colorless to yellow mineral crystallizing in the trigonal system. The prismatic crystals are typically colorless, turning white on partial dehydration. It is part of the ettringite-group which includes other sulfates such as thaumasite and bentorite.

Belite is an industrial mineral important in Portland cement manufacture. Its main constituent is dicalcium silicate, Ca2SiO4, sometimes formulated as 2 CaO · SiO2 (C2S in cement chemist notation).

Portlandite hydroxide mineral

Portlandite is an oxide mineral. It is the naturally occurring form of calcium hydroxide (Ca(OH)2) and the calcium analogue of brucite (Mg(OH)2).

The Maidens island in United Kingdom

The Maidens or Hulin Rocks are two islets and several skerries in the North Channel off County Antrim in Northern Ireland. The Eastern Maiden or Southern Rock lies about 9 km from the coast at Ballygalley, or 13 miles from Larne. The West Maiden or Northern Rock is about half a mile further out. Lighthouses were built on both rocks; the West Maiden was abandoned in 1903 and the East Maiden was automated in 1977.

Geology of Jersey

The geology of Jersey is characterised by the Late Proterozoic Brioverian volcanics, the Cadomian Orogeny, and only small signs of later deposits from the Cambrian and Quaternary periods. The kind of rocks go from conglomerate to shale, volcanic, intrusive and plutonic igneous rocks of many compositions, and metamorphic rocks as well, thus including most major types.

Pilot Knob (Austin, Texas) Eroded core of an extinct volcano located 8 miles (13 km) south of central Austin, Texas

Pilot Knob is the eroded core of an extinct volcano located 8 miles (13 km) south of central Austin, Texas, near Austin-Bergstrom International Airport and McKinney Falls State Park.

Larnite is a calcium silicate mineral with formula: Ca2SiO4. It is the calcium member of the olivine group of minerals.

Geology of the Isle of Skye

The geology of the Isle of Skye in Scotland is highly varied and the island's landscape reflects changes in the underlying nature of the rocks. A wide range of rock types are exposed on the island, sedimentary, metamorphic and igneous, ranging in age from the Archaean through to the Quaternary.

Scawtite cyclosilicate mineral

Scawtite is a hydrous calcium silicate mineral with carbonate, formula: Ca7(Si3O9)2CO3·2H2O. It crystallizes in the monoclinic crystal system as thin plates or flat prisms.