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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graphic [ign] (graph'-ic). Said of the texture of an igneous rock characterized by regular poikilitic intergrowth of triangular or linear-angular quartz grains within larger alkali feldspar grains. Similar intergrowths of other minerals, e.g. ilmenite-pyroxene, are less common. Syn: runic.

paleopedology . The study of paleosols or buried soils.

outwash drift . A deposit of outwash.

cat coal . Coal that contains pyrite.

electroviscosity (e-lec''-tro-vis-cos'-i-ty). The viscosity of a fluid as influenced by electric properties, e.g. greater viscosity of a low-conductivity fluid than of a high-conductivity fluid flowing through narrow capillaries.

snow cover . (a) All snow that has accumulated on the ground, including that derived from snowfall, drifting or blowing snow, avalanches, frozen or unfrozen rain stored in the snow, rime, and frost. (b) The areal extent of ground partly or wholly covered with snow in a particular area, usually expressed as a percent of the total area. (c) The average depth of accumulated deposited snow on the ground in a particular area, usually expressed in centimeters.

subalkaline basalt (sub-al'-ka-line). As proposed by Chayes (1964), a replacement for the terms tholeiitic basalt and tholeiite. Today it is the less preferred term. Basalts in which neither nepheline nor acmite appear in the CIPW norm fall in the subalkaline category.

ferrokentbrooksite . A red to reddish brown rhombohedral mineral of the eudialyte group: Na15Ca6Fe2+3Zr3Nb(Si25O73)(O,OH,H2O)3(F,Cl)2 .

crevice (crev'-ice). (a) A narrow opening or recess, as in a wave-eroded cliff or glacier. (b) A colloquial syn. of crevasse.

exocyathoid expansion (ex-o-cy'-a-thoid). Growth of an additional intervallum in an archaeocyathid cup, which appears to have had an adherent function (TIP, 1972, pt. E, p.7).

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