Diabase (), also called dolerite () or microgabbro, is a

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...

holocrystalline Crystallinity refers to the degree of structural order in a solid. In a crystal, the atoms or molecules are arranged in a regular, periodic manner. The degree of crystallinity has a large influence on hardness, density, transparency and diffusi ...

, subvolcanic rock equivalent to

volcanic A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often fo ...

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

or plutonic

gabbro Gabbro ( ) is a phaneritic (coarse-grained and magnesium- and iron-rich), mafic intrusive igneous rock formed from the slow cooling magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ch ...

. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grained to

aphanitic Aphanites (adj. ''aphanitic''; ) are igneous rocks that are so fine-grained that their component mineral crystals are not visible to the naked eye (in contrast to phanerites, in which the crystals are visible to the unaided eye). This geo ...

chilled margins which may contain tachylite (dark mafic glass). ''Diabase'' is the preferred name in North America, while ''dolerite'' is the preferred name in the rest of the English-speaking world, where sometimes the name ''diabase'' refers to altered dolerites and basalts. Some geologists prefer to avoid confusion by using the name ''microgabbro''. The name ''diabase'' comes from the French , and ultimately from the Greek 'act of crossing over, transition', whereas the name ''dolerite'' comes from the French , from the Greek 'deceitful, deceptive', because it was easily confused with

diorite Diorite ( ) is an intrusive rock, intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metals. It is Intermediate composition, inter ...

Petrography

Diabase normally has a fine but visible

texture Texture may refer to: Science and technology * Image texture, the spatial arrangement of color or intensities in an image * Surface texture, the smoothness, roughness, or bumpiness of the surface of an object * Texture (roads), road surface c ...

of euhedral

lath A lath or slat is a thin, narrow strip of straight-grained wood used under roof shingles or tiles, on lath and plaster walls and ceilings to hold plaster, and in lattice and trellis work. ''Lath'' has expanded to mean any type of backing m ...

-shaped

plagioclase Plagioclase ( ) is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continu ...

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

s (62%) set in a finer matrix of clinopyroxene, typically augite (20–29%), with minor

olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...

(3% up to 12% in olivine diabase),

magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula . It is one of the iron oxide, oxides of iron, and is ferrimagnetism, ferrimagnetic; it is attracted to a magnet and can be magnetization, magnetized to become a ...

(2%), and

ilmenite Ilmenite is a titanium-iron oxide mineral with the idealized formula . It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printi ...

(2%). Accessory and alteration

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

s include

hornblende Hornblende is a complex silicate minerals#Inosilicates, inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common ...

biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron- endmember annite, and the magnesium-endmember phlogopite; more al ...

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of Hydroxide, OH−, Fluoride, F− and Chloride, Cl− ion, respectively, in the crystal. The formula of the admixture of ...

pyrrhotite Pyrrhotite (''Pyrrhus of Epirus, pyrrhos'' in Greek language, Greek meaning "flame-coloured"'')'' is an iron sulfide mineral with the formula Fe(1−x)S (x = 0 to 0.125). It is a nonstoichiometric compound, nonstoichiometric variant of FeS, th ...

chalcopyrite Chalcopyrite ( ) is a copper iron sulfide mineral and the most abundant copper ore mineral. It has the chemical formula CuFeS2 and crystallizes in the tetragonal system. It has a brassy to golden yellow color and a Mohs scale, hardness of 3.5 to 4 ...

, serpentine,

chlorite The chlorite ion, or chlorine dioxide anion, is the halite (oxyanion), halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as s ...

, and

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

. The texture is termed ''diabasic'' and is typical of diabases. This diabasic texture is also termed ''interstitial''. The

feldspar Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocl ...

is high in

anorthite Anorthite (< ''an'' 'not' + ''ortho'' 'straight') is the

calcium

albite Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula . It is a tectosilicat ...

), the

calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...

endmember An endmember (also end-member or end member) in mineralogy is a mineral that is at the extreme end of a mineral series in terms of purity of its chemical composition. Minerals often can be described as solid solutions with varying compositions of ...

of the plagioclase anorthite-albite solid solution series, most commonly labradorite.

Locations

Diabase is usually found in smaller, relatively shallow intrusive bodies such as dikes and sills. Diabase dikes occur in regions of crustal extension and often occur in dike swarms of hundreds of individual dikes or sills radiating from a single

center. The Palisades Sill which makes up the New Jersey Palisades on the

Hudson River The Hudson River, historically the North River, is a river that flows from north to south largely through eastern New York (state), New York state. It originates in the Adirondack Mountains at Henderson Lake (New York), Henderson Lake in the ...

, near

New York City New York, often called New York City (NYC), is the most populous city in the United States, located at the southern tip of New York State on one of the world's largest natural harbors. The city comprises five boroughs, each coextensive w ...

, New York, United States, is an example of a diabase sill. The dike complexes of the British Tertiary Volcanic Province includes Skye, Rum, Mull, and Arran of western

Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...

, the Slieve Gullion region of

Ireland Ireland (, ; ; Ulster Scots dialect, Ulster-Scots: ) is an island in the North Atlantic Ocean, in Northwestern Europe. Geopolitically, the island is divided between the Republic of Ireland (officially Names of the Irish state, named Irelan ...

, and dolerite dike swarms extending across northern

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

towards the Midlands, for example Rowley Rag. Parts of the Deccan Traps of India, formed at the end of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

, also include dolerite. It is also abundant in large parts of

Curaçao Curaçao, officially the Country of Curaçao, is a constituent island country within the Kingdom of the Netherlands, located in the southern Caribbean Sea (specifically the Dutch Caribbean region), about north of Venezuela. Curaçao includ ...

, an island off the coast of

Venezuela Venezuela, officially the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and many Federal Dependencies of Venezuela, islands and islets in the Caribbean Sea. It com ...

. Another example of diabase dikes has been recognized in the Mongo area within the Guéra Massif of

Chad Chad, officially the Republic of Chad, is a landlocked country at the crossroads of North Africa, North and Central Africa. It is bordered by Libya to Chad–Libya border, the north, Sudan to Chad–Sudan border, the east, the Central Afric ...

in Central Africa. In the

Death Valley Death Valley is a desert valley in Eastern California, in the northern Mojave Desert, bordering the Great Basin Desert. It is thought to be the Highest temperature recorded on Earth, hottest place on Earth during summer. Death Valley's Badwat ...

region of California,

Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of t ...

diabase intrusions metamorphosed pre-existing dolomite into economically important

talc Talc, or talcum, is a clay mineral composed of hydrated magnesium silicate, with the chemical formula . Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening agent and lubricant ...

deposits. In the Thuringian-Franconian-Vogtland Slate Mountains of central

Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

the diabase is entirely of

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

age. They form typical domed landscapes, especially in the

Vogtland Vogtland (; ) is a region spanning the German states of Bavaria, Saxony and Thuringia and north-western Bohemia in the Czech Republic. It overlaps with and is largely contained within Euroregio Egrensis. The name alludes to the former leadershi ...

. One geotourist attraction is the '' Steinerne Rose'' near Saalburg, a natural monument, whose present shape is due to the typical weathering of lava pillows.

Gondwanaland and Australia

A geological event known as the Oenpelli Dolerite intrusive event occurred about 1,720 million years ago in western

Arnhem Land Arnhem Land is a historical region of the Northern Territory of Australia. It is located in the north-eastern corner of the territory and is around from the territorial capital, Darwin, Northern Territory, Darwin. In 1623, Dutch East India Compa ...

, in the

Northern Territory The Northern Territory (abbreviated as NT; known formally as the Northern Territory of Australia and informally as the Territory) is an states and territories of Australia, Australian internal territory in the central and central-northern regi ...

, forming curved ridges of Oenpelli Dolerite stretching over . Further west, on the northern coast of Arnhem Land, a "subsurface radial dyke swarm" known as Galiwinku Dolerite, taking its name from the Aboriginal name for Elcho Island, occurs on the Gove Peninsula and continues under the

Arafura Sea The Arafura Sea (or Arafuru Sea) lies west of the Pacific Ocean, overlying the continental shelf between Australia and Western New Guinea (also called Papua), which is the Indonesian part of the Island of New Guinea. Geography The Arafura Sea is ...

and on Wessel Islands, including Elcho and Milingimbi Islands. In the Yilgarn craton of

Western Australia Western Australia (WA) is the westernmost state of Australia. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to the south, the Northern Territory to the north-east, and South Australia to the south-east. Western Aust ...

, a

Proterozoic The Proterozoic ( ) is the third of the four geologic eons of Earth's history, spanning the time interval from 2500 to 538.8 Mya, and is the longest eon of Earth's geologic time scale. It is preceded by the Archean and followed by the Phanerozo ...

long dolerite dike, the Norseman-Wiluna greenstone belt is associated with the non-alluvial

gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...

mining area between Norseman and

Kalgoorlie Kalgoorlie-Boulder (or just Kalgoorlie) is a city in the Goldfields–Esperance region of Western Australia, located east-northeast of Perth at the end of the Great Eastern Highway. It is referred to as Kalgoorlie–Boulder as the surroundi ...

, which includes the largest gold mine in Australia, the Super Pit gold mine. West of the Norseman–Wiluna Belt is the Yalgoo-Singleton greenstone belt, where complex dolerite dike swarms obscure the volcaniclastic sediments. Large dolerite sills such as the Golden Mile Dolerite can exhibit coarse-grained texture, and show a large diversity in petrography and geochemistry across the width of the sill. The vast areas of mafic volcanism/

plutonism Plutonism is the geology, geologic theory that the igneous rocks forming the Earth originated from intrusive Magma, magmatic activity, with a continuing gradual process of weathering and erosion wearing away rocks, which were then deposited on t ...

associated with the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

breakup of the

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

supercontinent in the Southern Hemisphere include many large diabase/dolerite sills and dike swarms. These include the Karoo dolerites of

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

, the Ferrar Dolerites of

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...

, and the largest of these, the most extensive of all dolerite formations worldwide, are found in

Tasmania Tasmania (; palawa kani: ''Lutruwita'') is an island States and territories of Australia, state of Australia. It is located to the south of the Mainland Australia, Australian mainland, and is separated from it by the Bass Strait. The sta ...

. Here, the volume of

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...

which intruded into a thin veneer of

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

and

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

rocks from multiple feeder sites, over a period of perhaps a million years, may have exceeded 40,000 cubic kilometres. In Tasmania, dolerite dominates much of the landscape, particularly alpine areas, with many examples of

columnar jointing Columnar jointing is a geological structure where sets of intersecting closely spaced fractures, referred to as Joint (geology), joints, result in the formation of a regular array of polygonal Prism (geometry), prisms, or columns. Columnar join ...

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic� ...

activity resulted in the formation of dolerite intrusion in Prospect in

Sydney Sydney is the capital city of the States and territories of Australia, state of New South Wales and the List of cities in Australia by population, most populous city in Australia. Located on Australia's east coast, the metropolis surrounds Syd ...

, and quarrying of

for roadstone and other building materials has been an important activity there for over 180 years.

Use

Diabase is crushed and used as a

construction aggregate Construction aggregate, or simply aggregate, is a broad category of coarse- to medium-grained particulate material used in construction. Traditionally, it includes natural materials such as sand, gravel, crushed stone. As with other types of ag ...

for road beds, buildings, railroad beds (rail ballast), and within dams and levees. Diabase can be cut for use as

headstone A gravestone or tombstone is a marker, usually stone, that is placed over a grave. A marker set at the head of the grave may be called a headstone. An especially old or elaborate stone slab may be called a funeral stele, stela, or slab. The u ...

s and memorials; the base of the Marine Corps War Memorial is made of black diabase "granite" (a commercial term, not actual granite). Diabase can also be cut for use as ornamental stone for countertops, facing stone on buildings, and paving. A form of dolerite, known as

bluestone Bluestone is a cultural or commercial name for a number of natural dimension stone, dimension or building stone varieties, including: * basalt in Victoria (Australia), Victoria, Australia, and in New Zealand * diabase, dolerites in Tasmania, ...

, is one of the materials used in the construction of

Stonehenge Stonehenge is a prehistoric Megalith, megalithic structure on Salisbury Plain in Wiltshire, England, west of Amesbury. It consists of an outer ring of vertical sarsen standing stones, each around high, wide, and weighing around 25 tons, to ...

. Diabase also serves as local building stone. In Tasmania, where it is one of the most common rocks found, it is used for building, for landscaping and to erect dry-stone farm walls. In northern

County Down County Down () is one of the six counties of Northern Ireland, one of the nine counties of Ulster and one of the traditional thirty-two counties of Ireland. It covers an area of and has a population of 552,261. It borders County Antrim to the ...

, Northern Ireland, "dolerite" is used in buildings such as

Mount Stewart Mount Stewart is a 19th-century house and garden in County Down, Northern Ireland, owned by the National Trust. Situated on the east shore of Strangford Lough, a few miles outside the town of Newtownards and near Greyabbey, it was the Iris ...

together with Scrabo Sandstone as both are quarried at Scrabo Hill. Balls of diabase were used by the ancient Egyptians as pounding tools for working softer (but still hard) stones.

References

External links

Collection of dikes in the Fish River Canyon, Namibia
{{Authority control Aphanitic rocks Ophitic rocks Mafic rocks Subvolcanic rocks

Petrography

Locations

Gondwanaland and Australia

Use

See also

References

External links