RFG 2018 Conference

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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hydraulic action . The mechanical loosening and removal of weakly resistant material solely by the pressure and hydraulic force of flowing water, as by a stream surging into rock cracks or impinging against the bank on the outside of a bend, or by ocean waves and currents pounding the base of a cliff. See also: fluviraption.

thermal resistivity . The reciprocal of thermal conductivity, measured in meter kelvin per watt (m K W-1). Symbol: r.

brachylinear (brach-y-lin'-e-ar). "Any lineation....ranging in length from less than two kilometers to the lower limit of visibility of the unaided eye" (El-Etr, 1976, p.485).

spinodal decomposition . Exsolution that proceeds by small, pervasive compositional fluctuations that become increasingly divergent with time.

haldenhang (hal'-den-hang). A syn. of wash slope. Etymol: German "Haldenhang", "under-talus rock slope of degradation" (Penck, 1924).

olivine pyroxene melilitolite . In the IUGS classification, a plutonic rock consisting mostly of melilite, olivine, and clinopyroxene, with clinopyroxene > olivine.

thomsenolite (thom-sen'-o-lite). A white monoclinic mineral: NaCaAlF6•H2O .

megaflow mark (meg-a-flow'). A term used by Kuenen (1957, p.243) as a syn. of gouge channel.

pseudospondylium (pseu''-do-spon-dyl'-i-um). A cup-shaped chamber accommodating the ventral muscle field of a brachiopod and comprising an undercut callus contained between discrete dental plates. Cf: spondylium.

axial-plane cleavage . Cleavage that is, in the hinge of a fold, parallel to the hinge surface of the fold and whose intersection lineation with bedding is parallel to the fold hinge. Axial-plane cleavage may be everywhere parallel to the fold hinge surface, but normally cleavage fans or changes its orientation systematically with position about the fold. Cf: bedding-plane cleavage; fan cleavage; transecting cleavage.


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