{{short description|Lens-shaped igneous intrusion}} thumb|right|Cross-sectional diagram of phacoliths (red) in older folded rocks A '''phacolith''' is a pluton of igneous rock parallel to the bedding plane or foliation of folded country rock. More specifically, it is a typically lens-shaped pluton that occupies either the crest of an anticline or the trough of a syncline. In rare cases the body may extend as a sill from the crest of an anticline through the trough of an adjacent syncline, such that in cross section it has an ''S'' shape. In intensely folded terrain the hinge of folds would be areas of reduced pressure and thus potential sites for magma migration and emplacement.
The term was coined and initially defined by Alfred Harker in his ''The Natural History of Igneous Rocks'' in 1909.
==Examples== * in the Franklin and Hamburg areas of Sussex County, New Jersey, United States<ref name="BakerUSGS1970">{{cite book | title=Geology and Magnetite Deposits of the Franklin Quadrangle and Part of the Hamburg Quadrangle, New Jersey (USGS Professional Paper 638) | publisher=USGS | last1=Baker | first1=D.R. | last2=Buddington | first2=A.F. | url=https://pubs.usgs.gov/pp/0638/report.pdf | year=1970 | page=30 | location=Washington D.C.}}</ref> * the Omey pluton in Ireland<ref name="McCarthyEtAl2015">{{cite journal | url=https://www.cambridge.org/core/journals/earth-and-environmental-science-transactions-of-royal-society-of-edinburgh/article/late-caledonian-transpression-and-the-structural-controls-on-pluton-construction-new-insights-from-the-omey-pluton-western-ireland/1574E9D4256A4C623BA36B4F5C66C837 | title=Late Caledonian transpression and the structural controls on pluton construction; new insights from the Omey Pluton, western Ireland | first1=William | last1=McCarthy | first2=R. John | last2=Reavy | first3=Carl T. | last3=Stevenson | first4=Michael S. | last4=Petronis | journal=Earth and Environmental Science Transactions of the Royal Society of Edinburgh | year=2015 | volume=106 | issue=1 | pages=11–28 | doi=10.1017/S1755691015000201| bibcode=2015EESTR.106...11M | s2cid=132563143 | url-access=subscription }}</ref> * near Bayalan, Ajmer district, Rajasthan in India<ref name="Dasgupta2011">{{cite journal | title=Characteristics of pegmatoidal granite exposed near Bayalan, Ajmer district, Rajasthan | first1=N. | last1=Dasgupta | first2=T. | last2=Paljoydeep | first3=S. | last3=Ghosh | journal=Journal of Earth System Science | year=2011 | volume=120 | issue=4 | pages=617–626 | doi=10.1007/s12040-011-0100-7| bibcode=2011JESS..120..617D | doi-access=free }}</ref> *Corndon Hill, in Shropshire, England, United Kingdom<ref>{{Cite book|last=Leong|first=Goh Cheng|url=https://books.google.com/books?id=XhJ4RAAACAAJ&q=certificate+physical+and+human+geography|title=Certificate Physics And Human Geography; Indian Edition|date=1995-10-27|publisher=Oxford University Press|isbn=978-0-19-562816-6|pages=21|language=en}}</ref><ref name="EarpHains1971">{{cite book | url=https://webapps.bgs.ac.uk/Memoirs/docs/B01350.html | title=The Welsh Borderland | series=British Regional Geology | publisher=Her Majesty’s Stationery Office | first1=J.R. | last1=Earp | first2=B.A. | last2=Hains | date=1971 | edition=3rd | location=London}}</ref>
==See also== * Laccolith *Lopolith *Batholith
==References== {{Reflist}} *Davis A. Young (2003) ''Mind Over Magma: The Story of Igneous Petrology'', page 335, Princeton University Press. {{ISBN|0-691-10279-1}} *American Geological Institute. ''Dictionary of Geological Terms''. New York: Dolphin Books, 1962.
Category:Igneous rocks Category:Igneous petrology
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