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.

Subscribe via EMail to the GeoWord of the Day.

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.

bedding void . An open space between successive lava flows, formed where an overlying flow does not completely conform to the solidified crust of lava beneath it.

palimpsest [meta] . adj. Said of a structure or texture in a metamorphic rock in which remnants of some pre-existing structure or texture, perhaps even the original one, are preserved, and sometimes even megascopically visible. The term was first used by Sederholm (1891). Cf: relict [meta].


Subscribe to GeoWord of the Day