Editing Diabase

{{Short description|Type of igneous rock}}
[[File:Polished Diabase.jpg|thumb|Diabase]]
{{wikt | diabase}}

'''Diabase''' ({{IPAc-en|ˈ|d|aɪ|.|ə|ˌ|b|eɪ|s}}), also called '''dolerite''' ({{IPAc-en|ˈ|d|ɒ|l|.|ə|ˌ|r|aɪ|t}}) or '''microgabbro''',<ref name="Microgabbro">
{{cite web
 |url= http://www.bgs.ac.uk/bgsrcs/rcs_details.cfm?code=DOLR
 |title= BGS Rock Classification Scheme - Dolerite (Synonymous with Microgabbro)
 |publisher= British Geological Survey |access-date= 24 August 2015
}}
</ref> is a [[mafic]], [[holocrystalline]], [[subvolcanic rock]] equivalent to [[volcanic]] [[basalt]] or [[pluton]]ic [[gabbro]]. Diabase [[Dike (geology)|dike]]s and [[Sill (geology)|sill]]s are typically shallow intrusive bodies and often exhibit fine-grained to [[aphanitic]] [[chilled margin]]s 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 {{Lang|fr|diabase}}, and ultimately from the Greek {{Lang|el|διάβασις}} {{transliteration|el|diábasis}} 'act of crossing over, transition',<ref>{{oed|diabase}}</ref> whereas the name ''dolerite'' comes from the French {{Lang|fr|dolérite}}, from the Greek {{lang|el|δολερός}} {{transliteration|el|dolerós}} 'deceitful, deceptive', because it was easily confused with [[diorite]].

==Petrography==
[[File:Fair Head - geograph.org.uk - 817076.jpg|thumb|[[Fair Head]], Northern Ireland]]
Diabase normally has a fine but visible [[Rock microstructure|texture]] of [[euhedral]] [[lath]]-shaped [[plagioclase]] [[crystal]]s (62%) set in a finer matrix of [[pyroxene|clinopyroxene]], typically [[augite]] (20–29%), with minor [[olivine]] (3% up to 12% in olivine diabase), [[magnetite]] (2%), and [[ilmenite]] (2%).<ref>Klein, Cornelus and Cornelius S. Hurlbut Jr.(1986) ''[[iarchive:manualofmineralo00klei|Manual of Mineralogy]]'', Wiley, 20th ed., p. 483 {{ISBN|0-471-80580-7}}</ref> Accessory and alteration [[mineral]]s include [[hornblende]], [[biotite]], [[apatite]], [[pyrrhotite]], [[chalcopyrite]], [[serpentine group|serpentine]], [[chlorite group|chlorite]], and [[calcite]]. The texture is termed ''diabasic'' and is typical of diabases. This diabasic texture is also termed ''interstitial''.<ref>Morehouse, W. W. (1959) ''The Study of Rocks in Thin Section'', Harper & Row, p. 160</ref> The [[feldspar]] is high in [[anorthite]] (as opposed to [[albite]]), the [[calcium]] [[endmember]] of the plagioclase anorthite-albite solid solution series, most commonly [[labradorite]].

==Locations==
[[File:Dike diabase AZ.jpg|thumb|A diabase [[dike (geology)|dike]] crosscutting horizontal [[limestone]] beds in Arizona]]
[[File:Devil's Den 101215.jpg|thumb|Diabase boulders at [[Devil's Den]] on the [[Gettysburg Battlefield]], Pennsylvania, US]]
[[File:Doleritfelsen und Köcherbäume.jpg|thumb|Dolerite rocks and [[Quiver tree]]s near [[Keetmanshoop]] (Namibia)]]
[[File:Organ Pipes Mount Wellington.jpg|thumb|Dolerite forms tall vertical columns throughout [[Tasmania]]. These columns form steep vertical features through its alpine areas.]]

Diabase is usually found in smaller, relatively shallow intrusive bodies such as [[dike (geology)|dikes]] and [[sill (geology)|sill]]s. Diabase dikes occur in regions of [[crustal extension]] and often occur in [[dike swarm]]s of hundreds of individual dikes or sills radiating from a single [[volcanic]] center.

The [[Palisades Sill]] which makes up the [[New Jersey Palisades]] on the [[Hudson River]], near [[New York City]], 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]], the [[Slieve Gullion]] region of [[Ireland]], and dolerite dike swarms extending across northern [[England]] towards the Midlands, for example [[Rowley Rag]]. Parts of the [[Deccan Traps]] of India, formed at the end of the [[Cretaceous]], also include dolerite.<ref>[http://www.geokem.com/flood-basalts-1.html ''Continental Flood Basalts (and Layered Intrusions)'']</ref> It is also abundant in large parts of [[Curaçao]], an island off the coast of [[Venezuela]]. Another example of diabase dikes has been recognized in the [[Mongo, Chad|Mongo]] area within the [[Guéra Region|Guéra Massif]] of [[Chad]] in Central Africa.<ref>{{Cite journal|last1=Nkouandou|first1=Oumarou Faarouk|last2=Bardintzeff|first2=Jacques-Marie|last3=Mahamat|first3=Oumar|last4=Fagny Mefire|first4=Aminatou|last5=Ganwa|first5=Alembert Alexandre|date=2017-05-22|title=The dolerite dyke swarm of Mongo, Guéra Massif (Chad, Central Africa): Geological setting, petrography and geochemistry|journal=Open Geosciences|volume=9|issue=1|pages=138–150|doi=10.1515/geo-2017-0012|issn=2391-5447|bibcode=2017OGeo....9...12N|doi-access=free}}</ref>

In the [[Death Valley]] region of California, [[Precambrian]] diabase intrusions metamorphosed pre-existing [[Dolomite (mineral)|dolomite]] into economically important [[talc]] deposits.<ref>Miller, MB, and Wright, LA. 2007, "Geology of Death Valley National Park (Third Edition)", Kendall Hunt Publishing, p 19.</ref>

In the Thuringian-Franconian-Vogtland Slate Mountains of central [[Germany]] the diabase is entirely of [[Devonian]] age.<ref name="Deutsch2006">{{cite book | title=Einführung in die Geologie Deutschlands | publisher=Spektrum Akademischer Verlag | first1=Dierk | last1=Henningsen | first2=Gerhard | last2=Katzung | year=2006 | edition=7th | location=Munich | page=69 | isbn=3-8274-1586-1 | language=de}}</ref> They form typical domed landscapes, especially in the [[Vogtland]]. One [[Geotourism|geotourist]] attraction is the ''[[Steinerne Rose]]'' near [[Saalburg-Ebersdorf|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]], in the [[Northern Territory]],<ref>{{cite web|url=https://geoscience.nt.gov.au/gemis/ntgsjspui/bitstream/1/74562/1/EL5893_2008_P_01.pdf|title=Wellington Range Project Northern Territory EL 5893 Relinquishment Report|publisher=Cameco Australia Pty Lt|date=August 2008 |series=Report No.: WR08-02 |first1=Cath |last1=Ranford |first2=Paul|last2= Melville |first3=Craig|last3= Bentley|access-date=5 Oct 2020}}</ref> forming curved ridges of Oenpelli Dolerite stretching over {{convert|30,000| km2}}.<ref>{{cite web | website=Australian Stratigraphic Units Database|publisher= Australian Government. Geoscience Australia | title=Definition card for: Oenpelli Dolerite| url=http://dbforms.ga.gov.au/pls/www/geodx.strat_units.def?strno=14496&stratname=Oenpelli%20Dolerite | access-date=5 October 2020}} [[File:CC-BY icon.svg|50px]] Text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/3.0/au/ Attribution 3.0 Australia (CC BY 3.0 AU)] licence.</ref> Further west, on the northern coast of Arnhem Land, a "subsurface radial dyke swarm" known as [[Galiwinku]] Dolerite, taking its name from the [[Aboriginal Australian|Aboriginal]] name for Elcho Island, occurs on the [[Gove Peninsula]] and continues under the [[Arafura Sea]] and on [[Wessel Islands]], including Elcho and [[Milingimbi Island]]s.<ref>{{cite web | website=Australian Stratigraphic Units Database|publisher= Australian Government. Geoscience Australia | title=Definition card for: Galiwinku Dolerite| url=http://dbforms.ga.gov.au/pls/www/geodx.strat_units.def?strno=77145&stratname=Galiwinku%20Dolerite | access-date=5 October 2020}} [[File:CC-BY icon.svg|50px]] Text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/3.0/au/ Attribution 3.0 Australia (CC BY 3.0 AU)] licence.</ref>

In the [[Yilgarn craton]] of [[Western Australia]], a [[Proterozoic]] {{convert|200| km |adj=on}} long dolerite dike, the [[Norseman-Wiluna greenstone belt]]<ref>Hill R.E.T, [[Sarah-Jane Barnes|Barnes S.J.]], Gole M.J., and Dowling S.E., 1990. Physical volcanology of komatiites; A field guide to the komatiites of the Norseman-Wiluna Greenstone Belt, Eastern Goldfields Province, Yilgarn Block, Western Australia., Geological Society of Australia. {{ISBN|0-909869-55-3}}</ref> is associated with the non-alluvial [[gold]] mining area between [[Norseman, Western Australia|Norseman]] and [[Kalgoorlie]], which includes the largest gold mine in Australia,<ref>{{cite journal|doi=10.1144/1467-7873/07-132|author1=O'Connor-Parsons, Tansy |author2=Stanley, Clifford R. |title=Downhole lithogeochemical patterns relating to chemostratigraphy and igneous fractionation processes in the Golden Mile dolerite, Western Australia|year=2007|journal=Geochemistry: Exploration, Environment, Analysis|volume=7|issue=2|pages=109–27|bibcode=2007GEEA....7..109O |s2cid=140677224 }}</ref> 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.<ref>{{cite journal|author1=Wanga Q. |author2=Campbella I. H. |year= 1998|title= Geochronology of supracrustal rocks from the Golden Grove area, Murchison Province, Yilgarn Craton, Western Australia |journal=Australian Journal of Earth Sciences|doi=10.1080/08120099808728413|volume=45|issue=4|pages=571–77|bibcode = 1998AuJES..45..571W }}</ref> 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.<ref name="Travis_etal_1971">{{Citation|last1=Travis|first1=G.A.|last2=Woodall|first2=R.|last3=Bartram|first3=G.D.|chapter=The Geology of the Kalgoorlie Goldfield|editor-last=Glover|editor-first=J.E.|title=Symposium on Archaean Rocks|pages=175–190|publisher=Geological Society of Australia (Special Publication 3)|date=1971}}</ref>

The vast areas of mafic volcanism/[[plutonism]] associated with the [[Jurassic]] breakup of the [[Gondwana]] supercontinent in the [[Southern Hemisphere]] include many large diabase/dolerite sills and dike swarms. These include the [[Karoo]] dolerites of [[South Africa]], the [[Karoo-Ferrar|Ferrar Dolerite]]s of [[Antarctica]], and the largest of these, the most extensive of all dolerite formations worldwide, are found in [[Tasmania]]. Here, the volume of [[magma]] which intruded into a thin veneer of [[Permian]] and [[Triassic]] rocks from multiple feeder sites, over a period of perhaps a million years, may have exceeded 40,000 cubic kilometres.<ref>[[David Leaman|Leaman, David]] 2002, "The Rock that Makes Tasmania", Leaman Geophysics, {{ISBN|0-9581199-0-2}} p. 117.</ref> In Tasmania, dolerite dominates much of the landscape, particularly alpine areas, with many examples of [[columnar jointing]].

[[Early Jurassic]] activity resulted in the formation of [[Prospect dolerite intrusion|dolerite intrusion in Prospect]] in [[Sydney]],<ref>Jones, I., and Verdel, C. (2015). Basalt distribution and volume estimates of Cenozoic
volcanism in the Bowen Basin region of eastern Australia: Implications for a waning mantle plume. Australian Journal of Earth Sciences, 62(2), 255–263.</ref> and [[quarrying]] of [[basalt]] for [[roadstone]] and other building materials has been an important activity there for over 180 years.<ref name="Johnson1989">{{cite book|author=Robert Wallace Johnson|title=Intraplate Volcanism: In Eastern Australia and New Zealand|url=https://books.google.com/books?id=4NBOn7ecZeAC&pg=PA4|date=24 November 1989|publisher=Cambridge University Press|isbn=978-0-521-38083-6|pages=4–}}</ref><ref>Wilshire, H.G. (1967) The Prospect Alkaline Diabase-Picrite Intrusion New South Wales, Australia. Journal of Petrology 8(1) pp.97-163.</ref>

==Use==

Diabase is crushed and used as a [[construction aggregate]] for road beds, buildings, railroad beds (rail ballast), and within dams and levees.<ref>{{cite web|last1=Allen|first1=George|title=Clayton Quarry|url=http://www.mdia.org/site/mining/clayton-quarry|publisher=Mount Diablo Interpretive Association|date=Spring 2004|access-date=2017-03-30|archive-url=https://web.archive.org/web/20171116184525/http://www.mdia.org/site/mining/clayton-quarry|archive-date=2017-11-16|url-status=dead}}</ref><ref name="comparerocks">{{cite web|title=Diabase Rock|url=http://www.comparerocks.com/en/diabase-rock/model-82-0|publisher=comparerocks.com|access-date=2017-03-30|archive-url=https://web.archive.org/web/20170331115113/http://www.comparerocks.com/en/diabase-rock/model-82-0|archive-date=2017-03-31|url-status=dead}}</ref>

Diabase can be cut for use as [[headstone]]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.<ref name="comparerocks"/> A form of dolerite, known as [[bluestone]], is one of the materials used in the construction of [[Stonehenge]].<ref name="AGI_Stonehenge">{{cite web | url=https://www.earthmagazine.org/article/stonehenges-mysterious-stones | title=Stonehenge's Mysterious Stones | publisher=[[American Geosciences Institute]] | work=Earth magazine | date=31 December 2008 | access-date=8 November 2019 | first1=Brian S. | last1=John | first2=Lionel E. | last2=Jackson Jr.}}</ref>

Diabase also serves as local building stone. In Tasmania, where it is one of the most common rocks found,<ref name="TasVitiGeoMap">{{cite web | url=https://dpipwe.tas.gov.au/Documents/Geology3.pdf | title=Tasmanian Viticultural Soils and Geology | publisher=Tasmania Department of Primary Industries, Water and Environment / University of Tasmania / Tasmanian Institute of Agricultural Research | access-date=8 November 2019}}</ref> it is used for building, for landscaping and to erect [[Dry stone|dry-stone]] farm walls. In northern [[County Down]], Northern Ireland, "dolerite" is used in buildings such as [[Mount Stewart]] 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.<ref name="Pounders">{{cite journal | title = Dolerite pounders: Petrology, sources, and use | journal = Lithic Technology | volume = 35 | issue = 2 | year = 2010 | pages = 127–148 | last1 = Kelany | first1 = Adel | last2 = Harrell | first2 = James A. | last3 = Brown | first3 = V. Max | doi = 10.1080/01977261.2010.11721087 | jstor = 23273763 | s2cid = 127942498 | url = https://www.jstor.org/stable/23273763 | quote = Dolerite pounders are hand-held stone tools that were widely used in Egypt from the third to late first millennium BCE for quarrying and dressing granite and other hard rocks.| url-access = subscription }}</ref>

==See also==
* [[List of rock types]]
{{clear}}

==References==
{{Reflist|30em}}

==External links==
{{Commons category|Diabase}}
{{EB1911 poster|Diabase}}
*[https://maps.google.com/?ie=UTF8&ll=-27.798084,17.582932&spn=0.115559,0.222301&t=h&z=13 Collection of dikes in the Fish River Canyon, Namibia]

{{Igneous rocks}}
{{Rock type}}
{{Authority control}}

[[Category:Aphanitic rocks]]
[[Category:Ophitic rocks]]
[[Category:Mafic rocks]]
[[Category:Subvolcanic rocks]]