cataclastic rock . A rock, such as a tectonic breccia, containing angular fragments that have been produced by the crushing and fracturing of preexisting rocks as a result of mechanical forces in the crust; a metamorphic rock produced by cataclasis. Its fabric is a structureless rock powder. Pettijohn (1957, p.281) would include glacial till as a "cataclastic deposit" as it is "an extensive gouge caused by the grinding along the base of an overthrust ice sheet". See also: cataclasis [struc geol]; autoclastic rock; mylonite. Syn: cataclasite.
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.
activation energy . The extra amount of energy which any particle or group of particles must have in order to go from one energy state into another, such as changes in phase and movement of particles in diffusion. The greater the amount of energy involved, the higher the resistance to the change, or the potential barrier.
anthozoan (an-tho-zo'-an). Any coelenterate belonging to the class Anthozoa, which includes marine, polypoid, solitary or colonial, mostly sedentary forms and is characterized by the presence of a stomodaeum. Range, Ordovician to Holocene.
periodite (pe'-ri-od-ite''). A gradually and periodically changing sediment succession, most common in limestone-marl sequences. Periodites occur in environments free of tempestites and turbidites, as on an outer shelf or shallow basin below storm wave base, an isolated platform, or a deeper basin floor beyond the range of turbidites (Einsele and Seilacher, 1982, p.532).
lamalginite . An alginite with indistinct (microscopic) algal forms; a part of the liptinite maceral group.
ice table . A mass of level ice. Cf: sheet ice.
cuprosklodowskite (cu''-pro-sklo-dow'-skite). A strongly radioactive, greenish-yellow or grass-green, triclinic secondary mineral: (H3O)2Cu(UO2)2(SiO3OH)2•6H2O .
hydrometeor (hy-dro-me'-te-or). Any product of condensation or deposition in the atmosphere or on the Earth's surface. Precipitation, clouds, dew, and frost are hydrometeors.
dead water . In a stream, water that is or appears to be standing or still.
downgoing plate . At a convergent plate boundary, the plate that is being subducted and is sinking down into the mantle. Downgoing plates must be composed of oceanic lithosphere. Syn: slab.
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