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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forelimb (fore'-limb). The steeper of the two limbs of an asymmetrical, anticlinal fold. Cf: backlimb.

sappare (sap'-pare). (a) sapphire. (b) kyanite.

rattlesnake ore (rat'-tle-snake). A gray, black, and yellow mottled ore of carnotite and vanoxite, its spotted appearance resembling that of a rattlesnake.

semibituminous coal (sem''-i-bi-tu'-mi-nous). Coal that ranks between bituminous coal and semianthracite; it is harder and more brittle than bituminous coal. It has a high fuel ratio and burns without smoke. Syn: smokeless coal. Cf: metabituminous coal.

harmonic [geophys] . (a) A frequency which is a simple multiple of a fundamental frequency. The third harmonic, for example, has a frequency three times that of the fundamental. (b) Two frequencies are harmonically related if they are each harmonics of a common fundamental. (c) Any component of a Fourier series except the fundamental.

grain boundary sliding . A high-temperature deformation mechanism in fine-grained rocks whereby grains slip past one another along their grain boundaries, with compatibilities along grain boundaries being accommodated by solid-state diffusion creep or dislocation creep. The grain aggregate changes shape, but individual grains do not.

seismic efficiency . The percentage of earthquake-generated energy that goes into the production of elastic-wave energy.

ectinite (ec'-ti-nite). A rock formed as a result of essentially isochemical regional metamorphism, i.e., with no notable associated metasomatism (Dietrich and Mehnert, 1961). Rarely used.

tantalaeschynite-(Y) (tan-tal-aesch'-y-nite-y). A resinous brownish-black or black orthorhombic mineral of the aeschynite group: (Ca,Y,Ce)(Ta,Ti,Nb)2O6 .

Arctic [paleoclim] . The oldest subunit of the Blytt-Sernander sequence (Post, 1924), preceding the Preboreal, characterized primarily by tundra vegetation in Scandinavia, and recording the cold climate of full and late glacial time (prior to about 10,000 years B.P.). It is subdivided into Oldest Dryas, Bølling, Older Dryas, Allerød, and Younger Dryas. The term is rarely used.

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