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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ground roll . A seismic surface wave, generally of low frequency and velocity. Often considered to be a modified Rayleigh wave.

defect lattice (de'-fect). A crystal lattice in which the expected systemic repetition is interrupted by an omission, an inclusion of an extra item, or the substitution of an unexpected item. Cf: Schottky defect.

hetero- (het'-er-o-). A prefix meaning "different".

knap . (a) A crest or summit of a hill. (b) A small hill or slight rise of ground.

Orellan (O-rel'-lan). North American land mammal age: Upper Oligocene (after Chadronian, before Whitneyan).

porcelainite (por'-ce-lain-ite). (a) porcellanite. (b) mullite.

proton-precession magnetometer (pro'-ton-pre-ces'-sion). A type of nuclear resonance magnetometer that accurately measures absolute total magnetic intensity by the use of the precession of protons in a hydrogen-rich liquid (such as water) about the magnetic field direction. Precession frequency is proportional to field strength. See also: proton-vector magnetometer.

LO-analysis . A palynological method for analyzing the sculpture and structure of the sexine by comparing the elements in high and low focus. In high focus, raised elements are bright ("lux"), holes are dark ("obscuritas"). At low focus, this pattern is reversed.

soil mineralogy . The branch of soil science that deals with the homogeneous inorganic materials found in the Earth's crust to the depth of weathering or sedimentation.

Schoenflies notation (Schoen'-flies). A system of describing crystal classes by means of symbols used esp. by physicists and chemists. Cf: Hermann-Mauguin symbols. Syn: Schoenflies symbols; international symbols.

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