lens (geology)

{{Short description|Body of ore or rock that is thick in the middle and thin at the edges}}

File:Chalk_with_cover_of_Caliche_Naari_and_Chert_lens_a_road_38.jpg

In geology, a lens or lentil is a body of ore or rock that is thick in the middle and thin at the edges, resembling a convex lens in cross-section.{{cite book|last1=Bates|first1=Robert L.|last2=Jackson|first2=Julia A.|title=Dictionary of Geological Terms|location=New York|publisher=Anchor Press|date=1984|isbn=978-0385181013|url=https://books.google.com/books?id=m4iFpN2SpkEC|page=293}}

To thin out in all directions is to "lens out", also known as "lensing". The adjectives "lenticular" and "lentiform" are used to describe lens-like formations. Lenticle is a synonym for lentil, but may also refer to a fragment of rock that is lens-shaped. "Lenticule" is used for small lentil.{{cite book|last1=Neuendorf|first1=Klaus K. E.|last2=Jackson|first2=Julia A.|title=Glossary of Geology|location=Alexandria, Va.|publisher=American Geological Institute|date=2005|isbn=978-0922152766|url=https://books.google.com/books?id=yD79FqfECCYC|page=368}}

A lentil may also refer a minor unit in a formation of rock, similar to a member but not generally spread out over a large geographical area. In this usage, the lentil thins out towards its edges.{{cite book|last1=Koeberl|first1=Christian|last2=Martinez-Ruiz|first2=Francisca|title=Impact Markers in the Stratigraphic Record|location=Berlin|publisher=Springer Berlin|date=2013|isbn=978-3642624575|url=https://books.google.com/books?id=7WgrBgAAQBAJ|page=45}}

Lenticular bedding is a special form of rock interbedded mudrock and cross-laminated rippled sandstone. The lenses or ripples in lenticular beds are discontinuous in all directions.