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.


lava rag . An irregular-shaped bit of scoriaceous material ejected from a volcano.

pyroclast (py'-ro-clast). An individual particle ejected during a volcanic eruption. It is usually classified according to size. Cf: pyroclastic deposit.

thermocline [oceanog] . (a) The depth of the maximum rate of decrease of temperature with depth, the depth of the maximum of the vertical temperature gradient. (b) More generally, the region of large vertical temperature gradients below the mixed layer.

major fold . A large-scale or dominant fold in an area, with which minor folds are usually associated.

water-depth shallowing . In sequence stratigraphy, a decrease in water depth relative to a depositional surface. The shallowing may be caused by tectonic uplift, eustasy, or sedimentation onto the depositional surface.

pisoid . A round or ellipsoidal accretionary body commonly formed of calcium carbonate. A pisoid or pisolith is larger and less regular in form than an ooid, although it may have the same concentric and/or radial internal structure. Syn: pisolith; pisolite [sed].

ferroholmquistite . A theoretical orthorhombic member of the amphibole group, representing holmquistite with essential Fe2+: Li2(Fe2+3Al2)Si8O22(OH)2.

funnel filling (fun'-nel). The red-brown to dark-brown, opaque to translucent, coarsely laminated portion of the basal plate of some conodont elements, occupying the cavity in the basal funnel.

tungstic ocher (tung'-stic). (a) tungstite. (b) ferritungstite. Syn: wolfram ocher.

trichobothrium (trich-o-both'-ri-um). A sensory hair arising from the center of a disklike membrane on the legs or pedipalpi of an arachnid and serving for perception of air currents (TIP, 1955, pt. P, p.63). Also, a sensory organ consisting of one or more such hairs together with supporting structures. Pl: trichobothria.

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