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.

triangle (tri'-an-gle). An ordinarily plane figure bounded by three straight-line sides and having three internal angles. Cf: spherical triangle.

orbiculate (or-bic'-u-late). Said of a circular or disk-shaped leaf.

vitimite . A vitreous white monoclinic mineral: Ca₆B₁₄O₁₉(SO₄)(OH)₁₄•5H₂O.

pteromorph (pte'-ro-morph). An acritarch with a sphaeroidal vesicle (e.g., Pterospermella, Pterospermopsis ) surrounded by an equatorial flange. Most acritarchs of this type are believed to represent prasinophyte algae (Downie et al., 1963). See also: ala [palyn]; phycoma.

tableland (ta'-ble-land). (a) A general term for a broad, elevated region with a nearly level or undulating surface of considerable extent; e.g. South Africa. (b) A plateau bordered by abrupt clifflike edges rising sharply from the surrounding lowland; a mesa.

under side . Side of a conodont element toward which the basal cavity or basal pit opens (TIP, 1981, pt. W, supp.2). Syn: lower side.

élan vital (e-lan' vi-tal'). In early evolutionary theories, the internal vital or driving force that supposedly stimulates the process of evolution. It was regarded as an inherent property of living matter. Etymol: French.

pebble phosphate . A secondary phosphorite of either residual or transported origin, consisting of pellets, pebbles and nodules of phosphatic material mixed with sand and clay, as in Florida; e.g. land-pebble phosphate and river-pebble phosphate.

splay [struc geol] . A minor fault that branches off of a larger fault. Commonly major faults terminate in an array of splays. See also: horsetail [struc geol] .

inertite (in-ert'-ite). A microlithotype of coal that contains a combination of inertinite macerals totalling at least 95% (ICCP, 1971). Cf: fusite; liptite; vitrite.

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