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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lipogenesis (li-po-gen'-e-sis). In evolution, accelerated development as a result of the omission of certain ancestral stages. Cf: bradytely; tachytely.

marcasite [mineral] . A common metallic light yellow or grayish orthorhombic mineral: FeS2. It is dimorphous with pyrite and resembles it in appearance, but marcasite has a lower specific gravity, less chemical stability, and usually a paler color. Marcasite often occurs in sedimentary rocks (such as chalk) in the form of nodules or concretions with a radiating fibrous structure. Syn: white iron pyrites; iron pyrites; white pyrite; white pyrites; cockscomb pyrites; spear pyrites; lamellar pyrites.

gum . An organic, viscid juice extracted from, or exuded by, certain trees and plants. It hardens in the air and is soluble in water.

intergrade . (a) A taxonomic class at the subgroup level of soil taxonomy having properties typical of the great group of which it is a member and that are characteristic of some class in a higher category (any order, suborder, or great group) and indicates a transition to that kind of soil. (b) A soil that is amember of one such subgroup. See also: extragrade.

intergrade . (a) A taxonomic class at the subgroup level of soil taxonomy having properties typical of the great group of which it is a member and that are characteristic of some class in a higher category (any order, suborder, or great group) and indicates a transition to that kind of soil. (b) A soil that is amember of one such subgroup. See also: extragrade.

cryotexture . The textural characteristics of frozen, fine-grained organic and mineral earth materials cemented together with ice.

dissolved organic carbon . Carbon present in seawater in the form of dissolved organic molecules, i.e., the elemental carbon in dissolved organic matter. Abbrev: DOC.

rosette [paleont] . (a) A delicate calcareous plate formed of metamorphosed basal plates, centrally located within the radial pentagon in some free-swimming crinoids. (b) The group of five petal-shaped ambulacra on certain echinoids. (c) A cluster of parts in circular form; e.g. a discoaster. (d) A flower-shaped button within a hexagonal pore frame in a radiolarian skeleton. (e) The cellular part of a septula in cheilostome and ctenostome bryozoans.

balas ruby (bal'-as). A pale rose-red or orange gem variety of spinel, found in Badakhshan (or Balascia) province in northern Afghanistan. See also: ruby spinel. Syn: ballas.

Giggenbach bottle . An evacuated alkaline-solution-filled bottle (e.g., sodium hydroxide, NaOH), generally connected to a titanium or silica tube which is inserted into a fumarole. The gases bubble through the solution, condense, and are absorbed by the solution, which can be analyzed (William-Jones and Rymer, 2000).

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