heteropic (het-er-op'-ic). Said of sedimentary rocks of different facies, or said of facies characterized by different rock types. The rocks may be formed contemporaneously or in juxtaposition in the same sedimentation area or both, but the lithologies are different; e.g. facies that replace one another laterally in deposits of the same age. Also, said of a map depicting heteropic facies or rocks.
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.
stability field . The range of conditions within which a mineral or mineral assemblage is stable.
homalozoan (hom''-a-lo-zo'-an). Any echinoderm belonging to the subphylum Homalozoa, characterized by the absence of radial symmetry and having a basically asymmetrical body. The subphylum includes the carpoids and possibly the class Machaeridia.
sterlinghillite . A silky white to light pink monoclinic mineral: Mn2+3(AsO4)2•4H2O.
phloem . The food-conducting tissue of vascular plants, consisting of various types of cells, such as sieve tubes, phloem parenchyma, fibers, and companion cells.
alpha [mineral] . adj. Of or relating to one of two or more closely related minerals and specifying a particular physical structure (esp. a polymorphous modification); specif. said of a mineral that is stable at a temperature lower than those of its beta and gamma polymorphs (e.g. "alpha cristobalite" or "α-cristobalite", the low-temperature tetragonal phase of cristobalite). Some mineralogists reverse this convention, using α for the high-temperature phase (e.g. "alpha carnegieite", the isometric phase of carnegieite stable above 690°C).
permanent magnet . A magnet having a large, hard remanent magnetization.
erosion integral . An expression of the relative volume of a landmass removed by erosion at a given contour; the inverse of the hypsometric integral.
glass [ign] . An amorphous product of the rapid cooling of a magma. It may constitute the whole rock (e.g. obsidian) or only part of a groundmass. Cf: volcanic glass.
Atterberg grade scale (At'-ter-berg). A geometric and decimal grade scale devised by Albert Atterberg (1846-1916), Swedish soil scientist; it is based on the unit value 2 mm and involves a fixed ratio of 10 for each successive grade, yielding the diameter limits of 200, 20, 2.0, 0.2, 0.02, and 0.002 (Atterberg, 1905). Subdivisions are the geometric means of the grade limits. The scale has been widely used in Europe and was adopted in 1927 by the International Commission on Soil Science (but not by the U.S. Bureau of Soils).
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