Lens (geology)

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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. [1]

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. [2]

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. [3]

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. [2]

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<span class="mw-page-title-main">Gneiss</span> Common high-grade metamorphic rock

Gneiss is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures and pressures than schist. Gneiss nearly always shows a banded texture characterized by alternating darker and lighter colored bands and without a distinct cleavage.

<span class="mw-page-title-main">Lens</span> Optical device which transmits and refracts light

A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (elements), usually arranged along a common axis. Lenses are made from materials such as glass or plastic and are ground, polished, or molded to the required shape. A lens can focus light to form an image, unlike a prism, which refracts light without focusing. Devices that similarly focus or disperse waves and radiation other than visible light are also called "lenses", such as microwave lenses, electron lenses, acoustic lenses, or explosive lenses.

<span class="mw-page-title-main">Mafic</span> Silicate mineral or igneous rock that is rich in magnesium and iron

A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include basalt, diabase and gabbro. Mafic rocks often also contain calcium-rich varieties of plagioclase feldspar. Mafic materials can also be described as ferromagnesian.

<span class="mw-page-title-main">Schist</span> Easily split medium-grained metamorphic rock

Schist is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes or plates. This texture reflects a high content of platy minerals, such as micas, talc, chlorite, or graphite. These are often interleaved with more granular minerals, such as feldspar or quartz.

<span class="mw-page-title-main">Lithology</span> Description of its physical characteristics of a rock unit

The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lithology may refer to either a detailed description of these characteristics, or a summary of the gross physical character of a rock. Examples of lithologies in the second sense include sandstone, slate, basalt, or limestone.

<span class="mw-page-title-main">Lenticular cloud</span> Cloud species

Lenticular clouds are stationary clouds that form mostly in the troposphere, typically in parallel alignment to the wind direction. They are often comparable in appearance to a lens or saucer. Nacreous clouds that form in the lower stratosphere sometimes have lenticular shapes.

<span class="mw-page-title-main">Red Screes</span> Mountain in the English Lake District, Cumbria, England

Red Screes is a fell in the English Lake District, situated between the villages of Patterdale and Ambleside. It may be considered an outlier of the Fairfield group in the Eastern Fells, but is separated from its neighbours by low cols. This gives Red Screes an independence which is reflected in its prominence.

Lenticular is an adjective often relating to lenses. It may refer to:

<span class="mw-page-title-main">Lenticular lens</span>

A lenticular lens is an array of lenses, designed so that when viewed from slightly different angles, different parts of the image underneath are shown. The most common example is the lenses used in lenticular printing, where the technology is used to give an illusion of depth, or to make images that appear to change or move as the image is viewed from different angles.

<span class="mw-page-title-main">Basement (geology)</span> Metamorphic or igneous rocks below a sedimentary platform or cover

In geology, basement and crystalline basement are crystalline rocks lying above the mantle and beneath all other rocks and sediments. They are sometimes exposed at the surface, but often they are buried under miles of rock and sediment. The basement rocks lie below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin. In the same way, the sediments or sedimentary rocks on top of the basement can be called a "cover" or "sedimentary cover".

<span class="mw-page-title-main">Cross-bedding</span> Sedimentary rock strata at differing angles

In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The original depositional layering is tilted, such tilting not being the result of post-depositional deformation. Cross-beds or "sets" are the groups of inclined layers, which are known as cross-strata.

<span class="mw-page-title-main">Bed (geology)</span> Layer of sediment, sedimentary rock, or pyroclastic material

In geology, a bed is a layer of sediment, sedimentary rock, or volcanic rock "bounded above and below by more or less well-defined bedding surfaces". Specifically in sedimentology, a bed can be defined in one of two major ways. First, Campbell and Reineck and Singh use the term bed to refer to a thickness-independent layer comprising a coherent layer of sedimentary rock, sediment, or pyroclastic material bounded above and below by surfaces known as bedding planes. By this definition of bed, laminae are small beds that constitute the smallest (visible) layers of a hierarchical succession and often, but not always, internally comprise a bed.

<span class="mw-page-title-main">Cylindrical lens</span>

A cylindrical lens is a lens which focuses light into a line instead of a point, as a spherical lens would. The curved face or faces of a cylindrical lens are sections of a cylinder, and focus the image passing through it into a line parallel to intersection of the surface of the lens and a plane tangent to it along the cylinder's axis. The lens converges or diverges the image in the direction perpendicular to this line, and leaves it unaltered in the direction parallel to its cylinder's axis.

<span class="mw-page-title-main">Clarens Formation</span> Geological formation of the Stormberg Group in southern Africa

The Clarens Formation is a geological formation found in several localities in Lesotho and in the Free State, KwaZulu-Natal, and Eastern Cape provinces in South Africa. It is the uppermost of the three formations found in the Stormberg Group of the greater Karoo Supergroup rocks and represents the final phase of preserved sedimentation of the Karoo Basin.

<span class="mw-page-title-main">Sedimentary structures</span> Geologic structures formed during sediment deposition

Sedimentary structures include all kinds of features in sediments and sedimentary rocks, formed at the time of deposition.

<span class="mw-page-title-main">Bedford Shale</span> Geological formation in the United States

The Bedford Shale is a shale geologic formation in the states of Ohio, Michigan, Pennsylvania, Kentucky, West Virginia, and Virginia in the United States.

The Triassic Lockatong Formation is a mapped bedrock unit in Pennsylvania, New Jersey, and New York. It is named after the Lockatong Creek in Hunterdon County, New Jersey.

A lens is an optical element which converges or diverges light.

<span class="mw-page-title-main">Lenticular fabric</span>

A lenticular fabric is a lattice-like arrangement of lens-shaped materials formed into a thin layer. When the surface of the fabric is smooth, it often has a reflective and light-distorting appearance.

<span class="mw-page-title-main">Cleveland Shale</span> Geologic formation in the United States

The Cleveland Shale, also referred to as the Cleveland Member, is a shale geologic formation in the eastern United States.

References

  1. Bates, Robert L.; Jackson, Julia A. (1984). Dictionary of Geological Terms. New York: Anchor Press. p. 293. ISBN   978-0385181013.
  2. 1 2 Neuendorf, Klaus K. E.; Jackson, Julia A. (2005). Glossary of Geology. Alexandria, Va.: American Geological Institute. p. 368. ISBN   978-0922152766.
  3. Koeberl, Christian; Martinez-Ruiz, Francisca (2013). Impact Markers in the Stratigraphic Record. Berlin: Springer Berlin. p. 45. ISBN   978-3642624575.