GeoWord of the Day

The GeoWord of the Day is a free service of the American Geosciences Institute. All of the terms and definitions are from the Glossary of Geology, 5th Edition Revised.

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migrating inlet . A tidal inlet, such as that connecting a coastal bay with the open sea, that shifts its position laterally in the direction in which the dominant longshore current flows. It results from deposition on one side of the inlet, accompanied by erosion on the other.

pilate (pi'-late). This term ideally refers to clavate -like sculpture of sporomorphs, but it and such terms as "piliferous," "pilose," "pilum," "pila," and "pilosus" have been defined and applied so differently that they are preferably avoided.

self-potential method . An electrical exploration method in which one determines the spontaneous electrical potentials ( spontaneous polarization ) that are caused by primary chemical, heat, or fluid flow. Syn: spontaneous-potential method.

silex (si'-lex). (a) The French term for flint. (b) Silica; esp. quartz, such as a pure or finely ground form for use as a filler. (c) An old term formerly applied to a hard, dense rock, such as basalt or compact limestone. Etymol: Latin, "hard stone, flint, quartz". The term was used by Pliny for quartz.

play . The active exploration or leasing of land for petroleum or natural gas, based on a concept of the petroleum geology of an area.

azoproite (a-zo-pro'-ite). A black orthorhombic mineral of the ludwigite group: (Mg,Fe2+)2(Fe3+,Ti,Mg)BO5 .

single crystal diffractometer . An instrument, often automated and computerized, that facilitates the orientation of a single crystal for diffraction of X-rays (or neutrons) by any set of lattice planes, and subsequent measurement of the intensity of the diffracted beam.

ventral valve . The pedicle valve of a brachiopod.

basement fold . An obsolete term for a compressional structure (fold or thrust) that formed within a continent and affected the entire thickness of the continental crust. This obsolete term is the English translation of Argand's plis de fond.

mictite (mic'-tite). Coarsely composite rock formed as the result of contamination of a magma, by the incorporation and partial or complete assimilation of country-rock fragments, under conditions of relatively low temperature and probably at relatively high levels in the crust (Dietrich and Mehnert, 1961). Rarely used.