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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melaphyre (mel'-a-phyre). A term originally applied to any dark-colored porphyritic igneous rock but later restricted to altered basalt, esp. of Carboniferous and Permian age. Obsolete.

directional drilling (di-rec'-tion-al). The intentional drilling of a well at controlled departures from the vertical and at controlled azimuths, often utilizing a whipstock or a special downhole assembly with a bent (angled) subassembly and a turbine motor located close to the drill bit. It is done to establish multiple wells from a single location such as an offshore platform, and for other purposes. Cf: deviation [drill]; sidetracking.

convergent margin . A continental edge that is also a plate edge and is being deformed by collision with another plate; active margin.

soil forming processes . Processes that form soil horizons and depend on the relative influence of the soil formation factors.

helicospore (hel'-i-co-spore). A cylindric, spiral, or convolute, usually septate, asexual fungal spore. Cf: Saccardoan spore groups.

irarsite (ir-ar'-site). A metallic black cubic mineral of the gersdorffite group: (Ir,Ru,Rh,Pt)AsS . It forms a series with hollingworthite.

quake sheet . A well-defined bed resembling a slump sheet but produced by an earthquake and resulting in load casting without horizontal slip (Kuenen, 1958, p.20).

dictyonalia (dic''-ty-o-nal'-i-a). The sponge spicules of a dictyonal framework.

bixbyite (bix'-by-ite). A black cubic mineral: (Mn3+,Fe3+)2O3 . Syn: partridgeite; sitaparite.

Aegean (Ae-ge'-an). A European substage: lower substage of Ladinian Stage; Middle Triassic (above Spathian substage of Olenekian, below Bithynian).

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