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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ventifact (ven'-ti-fact). A general term introduced by Evans (1911) for any stone or pebble shaped, worn, faceted, cut, or polished by the abrasive or sandblast action of windblown sand, generally under desert conditions; e.g. a dreikanter. See also: windkanter. Syn: glyptolith; wind-worn stone; wind-cut stone; wind-polished stone; wind-grooved stone; wind-scoured stone; wind-shaped stone.

vale . (a) A lowland, usually containing a stream; e.g. the depression between two parallel cuestas. It often forms the wider and flatter part of a valley. (b) A rift valley or tectonic valley; e.g. the Vale of Arabia. (c) valley.

glacial-deposition coast (gla'-cial-de-po-si'-tion). A coast with partly submerged moraines, drumlins, and other glacial deposits.

needle tin ore . A variety of cassiterite with acute pyramidal forms.

plat [cart] . (a) A diagram drawn to scale, showing boundaries and subdivisions of a tract of land as determined by survey, together with all essential data required for accurate identification and description of the various units shown and including one or more certificates indicating due approval. It differs from a map in that it does not necessarily show additional cultural, drainage, and relief features. (b) A precise and detailed plan or map representing a township, private land claim, mineral claim, or other surveyed area, and showing the actual or proposed divisions, special features, or uses of the land. Syn: cadastral map. See also: plot.

quartzine (quartz'-ine). Chalcedony characterized by fibers having a positive crystallographic elongation (parallel to the c -axis). Also spelled: quartzin.

acron . The anteriormost part of the cephalon of a crustacean, carrying the eyes and antennules.

pool [water] . (a) A small, natural body of standing water, usually fresh; e.g. a stagnant body of water in a marsh, or a transient puddle in a depression following a rain, or a still body of water within a cave. (b) A small, quiet, rather deep reach of a stream, as between rapids or where there is little current. See also: plunge pool. (c) A body of impounded water, artificially confined above a dam or the closed gates of a lock.

run [ore dep] . n. A flat irregular ribbonlike orebody following the stratification of the host rock.

epidote (ep'-i-dote). (a) A yellowish-green, pistachio-green, or blackish-green mineral: Ca2Al2(Fe3+,Al)(SiO4)(Si2O7)O(OH) . It commonly occurs associated with albite and chlorite as formless grains or masses or as monoclinic crystals in low-grade metamorphic rocks (derived from limestones), or as a rare accessory constituent in igneous rocks, where it represents alteration products of ferromagnesian minerals. Syn: pistacite; arendalite; delphinite; thallite. (b) A name for a mineral group with an analogous formula, but with Ca partially replaced by rare-earth elements, and Fe3+ replaced by Al, Mn3+, V3+, Fe2+ or Mg.