phonolite

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Unusually, phonolite forms from magma with a relatively low silica content, generated by low degrees of partial melting (less than 10%) of highly aluminous rocks of the lower crust such as tonalite, monzonite and metamorphic rocks. Melting of such rocks to a very low degree promotes the liberation of aluminium, potassium, sodium and calcium by melting of feldspar, with some involvement of mafic minerals. Because the rock is silica-undersaturated, it has no quartz or other silica crystals, and is dominated by low-silica feldspathoid minerals more than feldspar minerals.

A few geological processes and tectonic events can melt the necessary precursor rocks to form phonolite. These include intracontinental hotspot volcanism,{{Cite journal|last1=Wiesmaier|first1=Sebastian|last2=Troll|first2=Valentin R.|last3=Carracedo|first3=Juan Carlos|last4=Ellam|first4=Robert M.|last5=Bindeman|first5=Ilya|last6=Wolff|first6=John A.|date=2012-12-01|title=Bimodality of Lavas in the Teide–Pico Viejo Succession in Tenerife—the Role of Crustal Melting in the Origin of Recent Phonolites|url=https://academic.oup.com/petrology/article/53/12/2465/1497678|journal=Journal of Petrology|language=en|volume=53|issue=12|pages=2465–2495|doi=10.1093/petrology/egs056|issn=0022-3530|doi-access=free}} such as may form above mantle plumes covered by thick continental crust. A-type granites and alkaline igneous provinces usually occur alongside phonolites. Low-degree partial melting of underplates of granitic material in collisional orogenic belts may also produce phonolites.

File:Petrology Igneous.svg

Phonolite is a fine-grained equivalent of nepheline syenite. They are products of partial melting, are silica-undersaturated, and have feldspathoids in their normative mineralogy.

Mineral assemblages in phonolite occurrences are usually abundant feldspathoids (nepheline, sodalite, hauyne, leucite and analcite) and alkali feldspar (sanidine, anorthoclase or orthoclase), and rare sodic plagioclase. Biotite, sodium-rich amphiboles and pyroxenes along with iron-rich olivine are common minor minerals. Accessory phases include titanite, apatite, corundum, zircon, magnetite and ilmenite.Blatt, Harvey and Robert J. Tracy, Petrology, Freeman, 2nd ed. 1996, p. 52, {{ISBN|0-7167-2438-3}}. Phonolite's characteristic dark color comes from its concentration of dark pyroxenes such as aegirine and augite.

Blairmorite is an analcite-rich variety of phonolite.{{cite book | url=http://publications.gc.ca/collections/collection_2017/rncan-nrcan/M44-93-1B.pdf | title=Analcite-bearing igneous rocks from the Crowsnest Formation, southwestern Alberta (Current Research report 93-B1) | publisher=Geological Survey of Canada | first1=T.D. | last1=Peterson | first2=K.L. |last2=Currie | year=1993 | pages=51–56}}{{cite book | title=An Introduction to the Rock-Forming Minerals | publisher=Mineralogical Society | first1=W.A. | last1=Deer | first2=R.A. | last2=Howie | first3=J. | last3=Zussman | year=2013 | location=London | isbn=9780903056274| edition=3rd }}

File:Dyke in Tsili.jpg in Ethiopia]]

Image:Phonolite Beemerville Complex NJ.jpg

Nepheline syenites and phonolites occur widely distributed throughout the worldWoolley, A.R., 1995. Alkaline rocks and carbonatites of the world., Geological Society of London. in Canada, Norway, Greenland, Sweden, the United Kingdom, the Ural Mountains, the Pyrenees, Italy, Eifel and Kaiserstuhl in Germany, Brazil, the Transvaal region, the Magnet Cove igneous complex of Arkansas, the Beemerville Complex of New Jersey,Eby, G. N., 2012, The Beemerville alkaline complex, northern New Jersey, in Harper, J. A., ed., Journey along the Taconic unconformity, northeastern Pennsylvania, New Jersey, and southeastern New York: Guidebook, 77th Annual [http://www.fcopg.org/ Field Conference of Pennsylvania Geologists], Shawnee on Delaware, PA, p. 85-91. as well as on oceanic islands such as the Canary Islands.{{cite journal|last1=Bryan|first1=S. E|last2=Cas|first2=R. A. F.|last3=Martı́|first3=J|title=Lithic breccias in intermediate volume phonolitic ignimbrites, Tenerife (Canary Islands): constraints on pyroclastic flow depositional processes|journal=Journal of Volcanology and Geothermal Research|date=May 1998|volume=81|issue=3–4|pages=269–296|doi=10.1016/S0377-0273(98)00004-3|bibcode=1998JVGR...81..269B}}

Phonolite is common across Europe, particularly within the Eifel Plateau and the Laacher See. It is also found in the Czech Republic and the Mediterranean area near Italy. For localities in the United States, phonolite can be found in the Black Hills Forest in South Dakokta. The most well known phonolite-composed natural structure is the Devil's Tower, found in Wyoming.

Nepheline-normative rocks occur in close association with the Bushveld Igneous Complex, possibly formed from partial melting of the wall rocks adjacent to that large ultramafic layered intrusion. Phonolite occurs in the related Pilanesberg Complex and Pienaars River Complex.{{cite book | title=Hydrothermal Mineral Deposits: Principles and Fundamental Concepts for the Exploration Geologist | publisher=Sringer-Verlag | author=Pirajno, Franco | year=1992 | location=Berlin | pages=267–269 | isbn=978-3-642-75673-3}}

File:Phonolite Porphyry of Devils Tower in Wyoming in USA - with scale.jpg

• Cripple Creek & Victor Gold Mine phonolite pipe in Colorado
• Baldface Mountain, west-central British Columbia, Canada
• Devils Tower, Wyoming, United States, an example of columnar-jointed phonolite{{Cite journal| doi = 10.1126/science.134.3487.1373| issn = 0036-8075| volume = 134| issue = 3487| pages = 1373 | last = Bassett| first = W. A.| title = Potassium-Argon Age of Devils Tower, Wyoming| journal = Science| date = October 1961| bibcode = 1961Sci...134.1373B| pmid=17807346| s2cid = 3101604}}
• Hoodoo Mountain, northwestern British Columbia, Canada
• Missouri Buttes, Crook County, northeast Wyoming, United States

• Bass Rock, North Berwick Law and Traprain Law in southeast Scotland, UKBGS map viewer http://mapapps.bgs.ac.uk/geologyofbritain/home.html
• Bořeň, northwestern Czech Republic
• Mont Gerbier de Jonc, Ardèche, France{{cite web | url=http://www.geopark-monts-ardeche.fr/decouvrir-le-geopark/decouvrir-les-geosites-geopark/volcans-des-sucs-geopark/gerbier-de-jonc-et-sources-de-la-loire-2324.html | title=Gerbier de Jonc et sources de la Loire | publisher=Geopark - Parc Naturel Régional des Monts d'Ardèche | work=Volcans des sucs | access-date=15 January 2017 | language=fr}}
• Montiferru, Sardinia
• Wolf Rock, Cornwall

• Jebel Nefusa, Libya{{cite journal|last1=Bausch|first1=W. M.|title=The central part of the Jebel Nefusa volcano (Libya) survey map, age relationship and preliminary results|journal=Geologische Rundschau|date=June 1978|volume=67|issue=2|pages=389–400|doi=10.1007/BF01802796|bibcode=1978GeoRu..67..389B|s2cid=140601047}}
• Mount Cargill, Dunedin, New ZealandMarshall, Patrick, 'The occurrence of a mineral hitherto unknown in the phonolites of Dunedin, New Zealand', 1929.
• Teide, a stratovolcano on the island of Tenerife{{cite journal|last1=Ablay|first1=G. J.|last2=Carroll|first2=M. R.|last3=Palmer|first3=M. R.|last4=Marti|first4=J.|last5=Sparks|first5=R. S. J.|title=Basanite-Phonolite Lineages of the Teide-Pico Viejo Volcanic Complex, Tenerife, Canary Islands|journal=Journal of Petrology|date=May 1998|volume=39|issue=5|pages=905–936|doi=10.1093/petroj/39.5.905|bibcode=1998JPet...39..905A|doi-access=free}}
• The phonolitic lava lake in Mount Erebus, Ross Island, Antarctica
• The 'Bellstone' in Saint Helena{{Cite web|url=https://sainthelenaisland.info/levelwood.htm#bellstone|title=Levelwood | Saint Helena Island Info: All about St Helena, in the South Atlantic Ocean}}

Phonolites can be of interest as dimension stone or as aggregate for gravels.

Rarely, economically mineralised phonolite-nepheline syenite alkaline complexes can be associated with rare-earth mineralisation, uranium mineralisation and phosphates, such as at Phalaborwa, South Africa.

Phonolite tuff was used as a source of flint for adze heads and such by prehistoric people from Hohentwiel and Hegau, Germany.Affolter, J., 2002, Provenance des silex préhistoriques du Jura et des régions limitrophes, Archéologie neuchâteloise, 28.

Phonolites can be separated into slabs of appropriate dimensions to be used as roofing tiles in place of roofing slate. One such occurrence is in the French Massif Central region such as the Haute Loire département.{{citation needed|date=July 2013}}

{{reflist|30em}}

• [https://books.google.com/books?id=K48ZMBWtoi4C&dq=phonolite+occurrences&pg=PA127 Woolley, A.R., Alkaline rocks and carbonatites of the world]

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Category:Igneous petrology

Category:Volcanic rocks

Category:Intermediate rocks