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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crystal-structure solution . The determination of the approximate fractional coordinates for the atoms of a crystal structure by any of several methods, usually involving diffraction data. Syn: structure solution.

volcanic rock . (a) A generally finely crystalline or glassy igneous rock resulting from volcanic action at or near the Earth's surface, either ejected explosively or extruded as lava; e.g. basalt. The term includes near-surface intrusions that form a part of the volcanic structure. See also: volcanics. Cf: plutonic rock. (b) A general term proposed by Read (1944) to include the effusive rocks and associated high-level intrusive rocks; they are dominantly basic. Cf: neptunic rock; plutonic rock.

mesonorm (mes'-o-norm). Theoretical calculation of normative minerals in metamorphic rocks of the mesozone from chemical analyses (Barth, 1959). Cf: catanorm; epinorm. See also: Niggli molecular norm.

ecocline (ec'-o-cline). A cline related to the gradation between two different niches.

structural crystallography . Study of the internal arrangement and spacing of atoms and molecules composing crystalline solids.

alkali-feldspar syenite . In the IUGS classification, a plutonic rock with Q between 0 and 5, and P/(A+P) less than 10.

foot [geol] . (a) The bottom of a slope, grade, or declivity. Cf: head [geomorph]. (b) That portion of the displaced material of a landslide that lies downslope from the toe of the surface of rupture (Varnes, 1978). (c) The lower bend of a fold or structural terrace. Syn: lower break.

hause . An English term for a pass, or a ridge connecting two higher elevations, or a narrow gorge (Whitney, 1888, p.137). Cf: hals. Syn: haws.

vladimirite (vlad-i-mir'-ite). A pale rose, colorless, or white monoclinic mineral: Ca5(AsO4)2(AsO3OH)2•5H2O .

sorted [pat grd] . Said of a nongenetic group of patterned ground features displaying a border of stones (including boulders) commonly surrounding or alternating with fines (including sand, silt, and clay). Ant: nonsorted.


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