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.

Subscribe via email to the GeoWord of the Day.

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).