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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luhite (lu'-hite). A calcite-rich dike rock with olivine and titanian augite in a groundmass of clinopyroxene, melilite, hauyne, nepheline, and calcite; a hauyne-melilite damkjernite or hauyne-nepheline alnoite. The rock was named by Scheumann in 1913 for Luh, Czech Republic. Obsolete.

beaked apex . The upper angle of tergum of a cirripede crustacean, produced into a long narrow point (TIP, 1969, pt. R, p.91).

Santernian (San-ter'-ni-an). An Italian substage: lower substage of regional Calabrian stage, lowermost Pleistocene (below Emilian substage).

micrinite (mic'-ri-nite). A maceral of coal within the inertinite group having a reflectance higher than that of associated vitrinite, without recognizable plant-cell structure, and occurring as discrete particles of size less than 2 micrometers, commonly about 1 micrometer. Cf: macrinite; residuum [coal].

space-frequency domain . The two-dimensional transform of a seismic section from location versus time to wave-number versus frequency.

water well . (a) A well that extracts water from the saturated zone or that yields useful supplies of water. (b) A well that obtains groundwater information or that replenishes groundwater. (c) A well drilled for oil but yielding only water.

areal geology (ar'-e-al). The geology of an area, esp. the spatial distribution and position of stratigraphic units, structural features, and surface forms. Cf: regional geology.

thorium-230-deficiency method . The calculation of an age in years for fossil coral or shell from 10,000 to 250,000 years old, based on the departure of ionium (thorium-230) from equilibrium with uranium-238 and uranium-234 as a result of carbonate recrystallization shortly after its formation or burial. The age depends on the growth toward the equilibrium ratio, which is directly related to the passage of time. Cf: uranium-series age method; thorium-230/protactinium-231 deficiency method. Syn: ionium-deficiency method.

topographic-bathymetric map (top-o-graph'-ic-bath-y-met'-ric). A map with both the relief of the land and the bottom of the offshore areas shown by contours. Contour intervals on land and on sea bottom may not be the same (USGS, 2002b, p.2-50 to 2-51).

prosogyrate (pros-o-gy'-rate). Said of the umbones (of a bivalve mollusk) curved so that the beaks point in the anterior or forward direction. Ant: opisthogyrate.

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