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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subalkaline basalt (sub-al'-ka-line). As proposed by Chayes (1964), a replacement for the terms tholeiitic basalt and tholeiite. Today it is the less preferred term. Basalts in which neither nepheline nor acmite appear in the CIPW norm fall in the subalkaline category.

ferrokentbrooksite . A red to reddish brown rhombohedral mineral of the eudialyte group: Na15Ca6Fe2+3Zr3Nb(Si25O73)(O,OH,H2O)3(F,Cl)2 .

crevice (crev'-ice). (a) A narrow opening or recess, as in a wave-eroded cliff or glacier. (b) A colloquial syn. of crevasse.

exocyathoid expansion (ex-o-cy'-a-thoid). Growth of an additional intervallum in an archaeocyathid cup, which appears to have had an adherent function (TIP, 1972, pt. E, p.7).

peg-leg multiple . A multiple reflection involving successive reflection at different interfaces so that its travel path is not symmetrical. Sometimes refers to short-path multiples within thin beds, which result in transferring energy from the front of a wavetrain and adding it back later, and sometimes to long-path multiples, which lead to separate events.

fels . A rarely used term applied to massive metamorphic rock lacking schistosity or foliation, e.g., calcsilicate fels (Winkler, 1967). Cf: granofels.

rock train . A term suggested by Kendall and Wroot (1924, p.448) for the rock material in "process of transport at the sides and in the middle of a glacier" and "subject to the dynamic forces of the glacier".

transposition . In structural petrology, disruption of preexisting fabric so that all fabric elements are rotated to a new orientation. Results in a transposition or transposed foliation.

pleural furrow . (a) A groove along the surface of a pleura of a trilobite. (b) A groove crossing the pleura of a merostome.

vanuralite (van-ur-al'-ite). A citron-yellow monoclinic mineral: Al(UO2)2(V2O8)(OH)•11H2O .