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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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.

ajkaite (aj'-ka-ite). A pale-yellow to dark reddish-brown, sulfur-bearing fossil resin found in brown coal. Also spelled: ajkite.

sketch map . A map drawn freehand from observation or from loose and uncontrolled surveys rather than from exact survey measurements, showing only the main features of an area. It preserves the essential space relationships, but does not truly preserve scale or orientation.

Anthropogene (An-thro'-po-gene). An informal term for the latest interval of the Cenozoic, formerly widely used in the former USSR in place of Quaternary. The term refers to the anthropological characterization of the "ice age" interval, but was later defined by a level in the Ukraine which is closely equivalent to the international GSSP base of the Pleistocene at about 1.8 Ma. Cf: Pleistogene.