phacolith

English

Etymology

Coined by English geologist Alfred Harker in 1909 as phacolite, from phaco- (“lens”) +‎ -lite or -lith (“rock”).

Noun

phacolith (plural phacoliths)

1. (geology) A lens-shaped mass that occurs in an anticlinal crest or synclinal trough.
   • 1947, Virgil Everett Barnes, Raymond Fillmore Dawson, George Ashworth Parkinson, Building Stones of Central Texas - Volume 19, page 21:

     This body is a phacolith intruded along the gneiss-schist boundary in the trough of a syncline that plunges 16° southeast.

   • 1964, Geological Survey Professional Paper, volume 501, page A-81:

     This bedding forms a distinctive stratigraphic sequence that may be traced from phacolith to phacolith throughout an area of 1,200 square miles.

   • 2007, Richard Huggett, Fundamentals of Geomorphology, page 120:

     Corndon Hill, which lies east of Montgomery in Powys, Wales, is a circular phacolith made of Ordovician dolerite (Figure 5.3b).