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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soil mineralogy . The branch of soil science that deals with the homogeneous inorganic materials found in the Earth's crust to the depth of weathering or sedimentation.

Schoenflies notation (Schoen'-flies). A system of describing crystal classes by means of symbols used esp. by physicists and chemists. Cf: Hermann-Mauguin symbols. Syn: Schoenflies symbols; international symbols.

peel technique . A method of preparing rock sections for study. A smooth surface is differentially etched with acid, and then covered with cellulose acetate or a similar liquid that will dry to a transparent film. When this film is peeled off, it brings with it a thin layer of rock substance, preserving this material in its original space relations. It may then be studied microscopically.

vanalite (van'-al-ite). A bright yellow-orange monoclinic mineral: NaAl8V10O38•30H2O .

anthrinoid (an'-thri-noid). Vitrinite that occurs in noncaking anthracites and that has a reflectance higher than 2.0% (ASTM, 1970, p.19). Cf: xylinoid; vitrinoid.

convection [meteorol] . (a) Transfer of heat by vertical movements within the Earth's atmosphere owing to density differences caused by heating from below. (b) The mixing and transport of properties other than heat. Cf: advection [meteorol].

monument [surv] . A natural or artificial physical structure that marks the location on the ground of a corner or other survey point; e.g. a pile of stones indicating the boundary of a mining claim, or a road or fence marking the boundary of real property. See also: boundary monument.

spilitization (spi''-lit-i-za'-tion). Albitization of a basalt to form a spilite.

Saurischia (Saur-is'-chi-a). One of the two orders of archosaurian reptiles commonly treated as dinosaurs, characterized by a triradiate pelvis. It includes bipedal predators (Carnosauria, Coelurosauria), quadrupedal long-necked herbivores (Sauropods), and presumptive ancestors of the latter (Prosauropoda). Range, Middle Triassic to Upper Cretaceous. Cf: Ornithischia.

principal point . (a) The foot of the perpendicular from the interior perspective center of a lens to the plane of the photograph; the geometric center of an aerial photograph, or the point where the optical axis of the lens meets the film plane in an aerial camera. Symbol: p. See also: fiducial mark; photograph center. Syn: center point. (b) Either of two points on the axis of a lens such that a ray from any point of the object directed toward one principal point will emerge from the lens in a parallel direction but directed through the other principal point. (c) The point at which a principal visual ray intersects a perspective plane.

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