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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Dinantian (Di-nan'-tian). European stage: Lower Carboniferous. It includes Tournaisian and Viséan.

pseudofibrous peat (pseu-do-fi'-brous). Peat that is fibrous in texture but that is plastic and incoherent. Cf: fibrous peat; amorphous peat.

orthometric correction (or-tho-met'-ric). A systematic correction that must be applied to a gravity-oriented measured difference of elevation because level surfaces at different elevations are not exactly parallel.

endotheca (en-do-the'-ca). A collective term for the dissepiments inside the wall of a scleractinian corallite. Cf: exotheca.

symmetrical fold (sym-met'-ri-cal). (a) A fold whose axial surface is perpendicular to the enveloping surface. (b) A fold whose limbs have the same angle of dip relative to the axial surface. Cf: asymmetric fold.

alivincular (al-i-vin'-cu-lar). Said of a type of ligament of bivalve mollusks (e.g. Ostrea ) in which the longer axis is transverse to the hinge axis, or that is not elongated in the longitudinal direction or necessarily situated entirely posterior to the beaks, but is located between the cardinal areas (where present) of the respective valves, with the lamellar component both anterior and posterior to the fibrous component.

ionic substitution (i-on'-ic). The replacement of one or more kinds of ion in a crystal structure by other kinds of generally similar size and charge. Syn: diadochy; proxying; substitution.

demonstrated resources . A term for the sum of measured resources plus indicated resources.

chartometer (char-tom'-e-ter). An instrument for measuring distances on charts or maps, such as the length of a stream in a drainage basin on a topographic map. See also: opisometer. Syn: map measurer.

auxiliary mineral . In the Johannsen classification of igneous rocks, a light-colored, relatively less abundant mineral such as apatite, muscovite, corundum, fluorite, or topaz.

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