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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buried channel (bur'-ied). An old channel concealed by surficial deposits; esp. a preglacial channel filled with glacial drift.

barkevikite (bar-ke-vik'-ite). A brownish or velvet-black monoclinic mineral of the amphibole group, near arfvedsonite in composition and appearance. An unnecessary name for an iron-bearing or ferropargasitic hornblende.

peridot (per'-i-dot). (a) A transparent to translucent green gem variety of olivine. Syn: peridote. (b) A yellowish-green or greenish-yellow variety of tourmaline, approaching olivine in color. It is used as a semiprecious stone. Syn: peridot of Ceylon.

marais (ma-rais'). A French term for swamp used in place names in certain localities of the U.S.

shore platform . A descriptive term for the horizontal or gently sloping surface produced along a shore by wave erosion; specif. a wave-cut bench. Also, sometimes used as a purely descriptive term for wave-cut platform. Cf: scar [geomorph].

springcreekite . A black rhombohedral mineral of the crandallite group: BaV3+3(PO4)2(OH,H2O)6.

block slope . A thin accumulation of usually angular blocks, on high mountains and in polar regions, on slopes of 5° to 25° (White, 1976, p.89). Cf: block field.

discontinuity surface . A minor break in the sedimentary column, chiefly intraformational but including interformational junctions that have not involved large-scale erosion. It is lower in rank than disconformity (Bromley, 1975). Cf: omission surface.

orthorhombic system (or-tho-rhom'-bic). One of the six crystal systems, characterized by three axes of symmetry that are mutually perpendicular and of unconstrained relative lengths. Cf: isometric system; tetragonal system; hexagonal system; monoclinic system; triclinic system. Syn: rhombic system.

directive couple (di-rec'-tive). A pair of mesenteries in the so-called dorsoventral plane (extending from the dorsal toward the ventral side) of a coral polyp, characterized by pleats on the opposite rather than the facing sides of the mesenteries.

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