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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Bureau International de l'Heure . The organization responsible, by international agreement, for coordinating the measurements of time by national observatories and for providing an internationally acceptable and common time. It is also responsible for maintaining the international atomic second. As part of its function, it calculates the position of the Earth's axis of rotation and changes in the Earth's rate of rotation. Abbrev: BIH.

diatexite (di-a-tex'-ite). A rock formed by diatexis. Var: diatectite.

salt meadow . A grassy tract subject to overflow by salt water.

blue band [sed] . The thin but persistent bed of bluish clay found throughout the Illinois-Indiana coal basin.

hard ore . A term used in the Lake Superior region for a compact, massive iron ore mainly composed of specular hematite and/or magnetite and containing more than 58% iron. Cf: soft ore.

colored stone (col'-ored). A gemstone of any species other than diamond. This usage illogically classifies all varieties of such species as colored stones, including colorless varieties, but does not include colored diamonds. However, it has proved a practicable and satisfactory classification.

idiochromatic (id''-i-o-chro-mat'-ic). Said of a mineral whose color is a result of a chromophore that is essential to the chemical composition of the mineral. Cf: allochromatic.

greigite (greig'-ite). A pinkish gray cubic mineral of the linnaeite group: Fe3S4 . Syn: melnikovite.

depression [surv] . (a) The angular distance of an object beneath the horizontal plane that passes through the observer. (b) The angular distance of a celestial object below the horizon.

fines [sed] . (a) Very small particles, esp. those smaller than the average in a mixture of particles of various sizes; e.g. the silt and clay fraction in glacial drift, or the fine-grained sediment that settles slowly to the bottom of a body of water. (b) An engineering term for the clay- and silt-sized soil particles (diameters less than 0.074 mm) passing U.S. standard sieve no. 200.

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