grain [eco geol] . A quarrymen's term for a plane of parting in a metamorphic rock, e.g. slate, that is perpendicular to the flow cleavage; or for a direction of parting in massive rock, e.g. granite. Cf: rift [eco geol].
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.
tabulation [palyn] . The pattern according to which the constituent plates of a dinoflagellate theca or cyst are arranged (Evitt, 1970; Williams et al., 2000, p.223).
exponentiate (ex-po-nen'-ti-ate). To use an empirically derived exponential time-dependent gain in seismic playback.
blind zone . (a) A layer that cannot be detected by refraction seismic methods, also called "hidden layer". It may have a velocity lower than that of shallower refractors, which will lead to an overestimate of the depth of deeper refractors; or it may have a velocity intermediate between those of layers above and below but with insufficient velocity difference or thickness to produce first arrivals, thus tending to cause an underestimate of the depth of deeper refractors. (b) A zone from which reflections do not occur; a shadow zone. (c) A portion of a volume that is not illuminated by seismic energy with given source/receiver geometry.
cave system . (a) A group of caves that are connected or hydrologically related. (b) A complex cave. Syn: cavern system.
microgranular [sed] . Minutely granular; specif. the texture of a carbonate sedimentary rock wherein the particles are mostly 10-60 micrometers in diameter and are well-sorted, and the finer clay-sized matrix is absent (Thomas, 1962). Also said of a sedimentary rock with such a texture. Cf: micrograined.
lithiotantite (lith''-i-o-tan'-tite). A colorless monoclinic mineral: Li(Ta,Nb)3O8 .
dorsal area . The part of the whorl of a coiled cephalopod conch in contact with the preceding whorl (TIP, 1964, pt. K, p.55).
vertical gradiometer . An instrument for measuring the vertical gradient of a potential field.
apparent horizon . The visible line of demarcation between land or sea and sky. Strictly, it is the circle that bounds the part of the Earth's surface which would be visible from a given point if no irregularities or obstructions were present. The apparent horizon is extended slightly downward because of atmospheric refraction. In popular usage, the term horizon usually signifies the "apparent horizon". Cf: true horizon. Syn: visible horizon; local horizon; sensible horizon; geographic horizon; topocentric horizon; natural horizon.
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