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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megaclone (meg'-a-clone). A large, smooth monaxonic desma (of a sponge), having branches that bear cuplike articular facets, mostly terminal.

pseudoboléite (pseu-do-bo'-lé-ite). A blue tetragonal mineral: Pb31Cu24Cl62(OH)48 . Also spelled: pseudoboleite.

tectono-eustasy (tec'-ton-o-eu'-sta-sy). Worldwide change of sea level produced by a change in the capacity of the ocean basins owing to plate tectonic motions, e.g. sea-floor spreading, subduction. Term introduced by Fairbridge (1961, p.111). Cf: glacio-eustasy; sedimento-eustasy. Syn: diastrophic eustatism; tectono-eustatism.

blue hole . (a) A subsurface void developed in carbonate banks and islands, also offshore. It is open to the Earth's surface; contains tidally influenced waters of fresh, marine, or mixed chemistry; extends below sea level for the majority of its depth; and may provide access to cave passages (Mylroie et al., 1995). Cf: inland blue hole; ocean hole. (b) An obsolete term for a resurgence.

deglaciation (de''-gla-ci-a'-tion). The uncovering of a land area from beneath a glacier or ice sheet by the withdrawal of ice due to shrinkage by melting or calving of icebergs. As used in Great Britain, the term is restricted to a process that occurred in the past, in contrast to deglacierization. Also, the result of deglaciation.

zeophyllite (ze-o-phyll'-ite). A pearly white rhombohedral mineral: Ca13Si10O28(OH)2F10•6H2O . It sometimes contains iron.

mesopore [petrology] . In the pore-size classification of Choquette and Pray (1970, p.233), an equant to equant-elongate pore or a tubular or platy pore with an average diameter or thickness between 4 and 1/16 mm. Cf: megapore; micropore.

floodplain splay . A small alluvial fan or other outspread deposit formed where an overloaded stream breaks through a levee (artificial or natural) and deposits its material (often coarse-grained) on the floodplain. Syn: overbank splay; sand splay; channel splay; splay [geomorph].

International Years of the Quiet Sun . An international cooperative program during 1964-1965 of studying solar-terrestrial phenomena during a quiet-sun, i.e. sunspot-minimum, period. It is related to the International Geophysical Year and to the International Active Sun Years. Abbrev: IQSY.

geologese (ge-ol''-o-gese'). (a) Literary style or jargon peculiar to geologists. (b) Geological language that is "progressing rapidly" toward the construction of "sentences in such a way that their meaning is not apparent on first reading" (Vanserg, 1952, p.221).