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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sister group (sis'-ter). (a) Within a cladogram, any pair of taxa united at a single node. (b) In cladistic analysis, the group of organisms that is genealogically most closely related to the study group taxa, or ingroup (Brooks et al., 1984, p.81; Wiley et al., 1991, p.4). Cf: outgroup, ingroup.

iron froth . A fine, spongy or micaceous variety of hematite.

epiphysis [intrus rocks] (e-piph'-y-sis). An apophysis or tongue of a larger intrusion. Obsolete.

chlormanganokalite (chlor-man''-ga-no-ka'-lite). A yellow rhombohedral mineral: K4MnCl6 . The manganese analogue of rinneite.

soil color . Described with notations and descriptively from the Munsell color book. In addition to the dominant color (matrix), secondary colors ( mottles, redoximorphic features ) are described in terms of abundance, size, and contrast.

grimselite (grim'-sel-ite). A yellow hexagonal mineral: K3Na(UO2)(CO3)3•H2O .

font . An archaic term for a stream or a spring, fountain, or source of a stream; it forms part of place names, such as Chalfont.

genal spine . A spine extending backward from the genal angle of the cephalon of a trilobite, produced on the outer posterior margin of the free cheek.

belonosphaerite (bel''-o-no-sphae'-rite). An obsolete term for a spherulite whose minerals are in radial arrangement.

stratiform nickel-copper deposit . A mineral-deposit type characterized by stratiform nickel and copper sulfide minerals in the basal portion of layered mafic-ultramafic intrusive complexes. Syn: Stillwater-type nickel-copper deposit.


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