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.


odinite [mineral] . A silky green, 1:1 serpentine type clay mineral that is intermediate between dioctahedral and trioctahedral: (Fe3+,Mg,Al,Fe2+)2.4(Si,Al)2O5(OH)4. It crystallizes in trigonal and monoclinic polytypes. Apparently it forms in association with organic material on shallow marine shelves and reef lagoons in tropical latitudes (Bailey, 1988).

micro- (mi'-cro-). A prefix meaning "small". When modifying a rock name, it signifies fine-grained hypabyssal, as in microgranite. Cf: macro-.

garbenschiefer (gar'-ben-schief''-er). (a) feather amphibolite. (b) A type of spotted slate characterized by concretionary spots whose shape resembles that of a caraway seed. Etymol: German. Cf: knotenschiefer; fleckschiefer; fruchtschiefer.

uralite (ur'-al-ite). A green, generally fibrous or acicular variety of secondary amphibole (hornblende or actinolite) occurring in altered rocks and pseudomorphous after pyroxene (such as augite).

inactive volcano (in-ac'-tive). A volcano that has not been known to erupt. Cf: active volcano; dormant volcano; extinct volcano.

pingguite . A yellowish-green orthorhombic mineral: Bi6(Te4+)2O13.

cutter [karst] . A solution-widened fracture. Depths range up to tens of meters. It may or may not be soil covered. Cf: karren; grike.

plane jet . A flow pattern characteristic of hyperpycnal inflow, in which the inflowing water spreads as a parabola whose width is about three times the square root of the distance downstream from the mouth (Moore, 1966, p.87). Cf: axial jet.

cyclic terrace . One of several stream terraces representing former valley floors formed during periods when downcutting had essentially stopped for a time and lateral erosion had become dominant; e.g. a valley-plain terrace. Terraces on opposite sides of the valley are paired or correspond in altitude along any given section of the valley. Cf: noncyclic terrace.

hole [streams] . (a) A deep place in a stream. (b) A water hole in the bed of an intermittent stream.

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