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.


earlshannonite (earl-shan'-non-ite). A reddish-brown monoclinic mineral of the whitmoreite group: (Mn2+,Fe2+)Fe3+2(PO4)2(OH)2•4H2O . It is the Mn-analogue of whitmoreite.

barbosalite (bar-bo'-sa-lite). A dark blue-green to black monoclinic mineral: Fe2+Fe3+2(PO4)2(OH)2 . It is also known as "ferrous ferric lazulite". A member of the lazulite group.

sherd . A fragment or broken piece of pottery. Syn: shard.

ray [paleont] . (a) Any of the radiating divisions of the body of an echinoderm together with all structures borne by it; e.g. a segment of an echinoderm body that includes one ambulacral axis, or a radial plate or an arm of a crinoid. Also, a radial direction established by the position of an ambulacrum. (b) One of the primary subdivisions of a sponge spicule containing an axial filament or an axial canal. (c) In Osteichthyes and Chondrichthyes, one of many fine rods, respectively bony or horny, that support a fin.

subgrain boundary . A planar crystal defect bounding a subgrain consisting of a low angle boundary separating parts of a crystal whose lattices are tilted at low angles with respect to one another. The boundary is defined by a concentration of dislocations . Syn: tilt boundary.

afwillite (af-wil'-lite). A colorless monoclinic mineral: Ca3(SiO3OH)2•2H2O .

environmental science . A multi-disciplinary field of study, often founded within geology, biology or cultural programs, that incorporates aspects of life, social, and earth science courses to deal with (1) social and political decision making and policy setting relative to the environment or environmental ethics, (2) the planning and management of natural and human resources with an emphasis on the social and political aspects, and (3) legal and regulatory aspects of environmental protection activities carried out by the government under its police powers.

niningerite (nin'-in-ger-ite''). A metallic gray cubic meteorite mineral of the galena group: (Mg,Fe2+,Mn)S .

syntectonic joints . Joints associated with intense deformation, associated with mountain building processes (Bahat, 1991). These are distinguished from regional joint sets which form on stable continental platforms.

perroudite (per-roud'-ite). An adamantine red orthorhombic mineral: Hg2+4Ag4S5(Cl,I,Br)4 .

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