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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orbitoid (or'-bi-toid). Any foraminifer belonging to the superfamily Orbitoidacea, characterized by large discoidal saddle-shaped or stellate tests with walls composed of radially arranged calcite crystals and with bilamellid septa. Range, Cretaceous to Holocene.

coparsite . A metallic black orthorhombic mineral: Cu4O2(As,V)O4Cl.

angulate element . An arched pectiniform conodont element with two primary processes, which are anterior and posterior (TIP, 1981, pt. W, supp.2).

dynamogranite (dy''-na-mo-gran'-ite). A seldom-used term for an augen gneiss containing much microcline and orthoclase (Krivenko and Lapchik, 1934).

Permian (Per'-mi-an). The uppermost system of the Paleozoic Erathem of the Standard Global Chronostratigraphic Scale, above the Carboniferous and below the Triassic System of the Mesozoic Erathem. Also the time during which these rocks were formed, the Permian Period, covering the time span between 295 and 250 Ma. It is named after the province of Perm, Russia, where rocks of this age were first studied.

wave-built terrace . A gently sloping coastal feature at the seaward or lakeward edge of a wave-cut platform, constructed by sediment brought by rivers or drifted along the shore or across the platform and deposited in the deeper water beyond. Cf: marine terrace; beach plain. Syn: wave-built platform.

wind-polished stone (wind'-pol-ished). A ventifact having a desert polish.

formation evaluation . The process of evaluating gas- or oil-bearing formations penetrated by a well or wells, and of appraising their commercial significance.

interval scale . A continuous scale of measurement that has an arbitrary origin and in which the differences between successive units of the scale are constant. The Celsius and Fahrenheit temperature scales are classic examples. Cf: nominal scale; ordinal scale; ratio scale.

suspension feeder . An animal that obtains its food by removing particulate organic matter from water, but not necessarily through the use of a filter. Cf: filter feeder.