gabbro


gabbro
gabbroic /geuh broh"ik/, gabbroitic, adj.gabbroid /gab"royd/, adj.
/gab"roh/, n., pl. gabbros. Petrol.
a dark granular igneous rock composed essentially of labradorite and augite.
[ < It; akin to L glaber smooth]

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Any of several medium-or coarse-grained rocks that consist primarily of plagioclase feldspar and pyroxene.

Gabbros are found widely on the Earth and on the Moon. They are sometimes quarried for dimension stone ("black granite"), but the direct economic value of gabbro is minor. Far more important are the nickel, chromium, and platinum minerals that occur almost exclusively in association with gabbroic or related rocks. Magnetite (iron) and ilmenite (titanium) are also found in gabbroic complexes.

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rock
 any of several medium- or coarse-grained rocks that consist primarily of plagioclase feldspar and pyroxene. Essentially, gabbro is the intrusive (plutonic) equivalent of basalt, but whereas basalt is often remarkably homogeneous in mineralogy and composition, gabbros are exceedingly variable. Gabbros are found widely on the Earth and on the Moon as well. Gabbros are sometimes quarried for dimension stone (the black granite of commerce), and the San Marcos Gabbro of southern California is used for gauge blocks, but the direct economic value of gabbro is minor. Far more important are the primary mineralizations of nickel, chromium, and platinum that occur almost exclusively in association with gabbroic or related ultramafic (very silica-poor) rocks. Primary magnetite (iron) and ilmenite (titanium) mineralizations are often intimately associated with gabbroic complexes.

      Banded, or layered, gabbroic complexes in which monomineral or bimineral varieties are well developed have been described from Montana, the Bushveld in South Africa, and the island of Skye. There are also gabbro complexes that are locally streaky and inhomogeneous and are not regularly layered, as the large, basinlike intrusion at Sudbury, Ont., and some of the larger diabase sills (tabular intrusions), as at Beaver Bay, Minn.; the Palisades, New Jersey; and many of the Karoo (Karroo) diabases in South Africa.

      A lopolith at Duluth, Minn., is a notable exception to the rather arbitrary division between layered and unlayered gabbro complexes. The lower part of this mass has the average composition of an olivine gabbro but is strongly banded, with individual bands that vary in composition from anorthosite to peridotite (monomineralic rocks that contain labradorite and olivine). The upper portion is a comparatively homogeneous feldspathic gabbro, locally patchy and streaky but not sharply banded. Between the two major divisions, and again at the top of the feldspathic gabbro, is a zone of granophyre or micropegmatitic granite.

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Universalium. 2010.

Look at other dictionaries:

  • Gabbro — (pronEng|ˈɡæbrəʊ) is a dark, coarse grained, intrusive igneous rock chemically equivalent to basalt. It is a plutonic rock, formed when molten magma is trapped beneath the Earth s surface and cools into a crystalline mass. The vast majority of… …   Wikipedia

  • gabbro — [ gabro ] n. m. • 1778; mot florentin, p. ê. du nom d un village toscan ♦ Géol. Roche éruptive composée de plagioclases et de pyroxène. ● gabbro nom masculin (de Gabbro, nom propre) Roche plutonique basique constituée essentiellement de… …   Encyclopédie Universelle

  • Gabbro — Gabbro, in der Gesteinskunde ein granitisch körniges Gestein, das vorwiegend aus Feldspat und Diallag besteht, zu denen sich noch in einigen Arten der Olivin (Olivingabbro) als wesentlicher Gemengteil gestellt. Der Feldspat bildet meist größere,… …   Lexikon der gesamten Technik

  • gabbro — GABBRÓ s.n. v. gabro. Trimis de LauraGellner, 13.09.2007. Sursa: DN  gabró/gabróu s. n. rocă magmatică intruzivă cu structură holocristalină, din feldspaţi plagioclazi, piroxeni, amfiboli, olivinã şi biotit, folosit în construcţii şi în pavaje.… …   Dicționar Român

  • Gabbro — Gab bro, n. [It.] (Geol.) A name originally given by the Italians to a kind of serpentine, later to the rock called {euphotide}, and now generally used for a coarsely crystalline, igneous rock consisting of lamellar pyroxene (diallage) and… …   The Collaborative International Dictionary of English

  • gabbro — (n.) type of igneous rock, 1837, from It. (Tuscan) gabbro, from L. glaber bare, smooth, bald (see GLAD (Cf. glad)) …   Etymology dictionary

  • Gabbro — (Geogn.), ein körniges Gemenge von Diallag u. Labrador; gehört zu den plutonischen Gebirgsarten u. kommt häufig in Begleitung des Serpentins vor. Früher bezog man ihn von der Insel Corsica u. verarbeitet ihn zu Tischplatten u. anderen… …   Pierer's Universal-Lexikon

  • Gabbro — (Euphotid), massiges kristallinisches Gestein von meist grobkörniger, selten flaseriger (Flasergabbro) Struktur, besteht aus einem basischen Kalknatronfeldspat (Labrador bis Anorthit) und Diallag, zu denen als weiterer Gemengteil oft noch Olivin… …   Meyers Großes Konversations-Lexikon

  • Gabbro — Gabbro, körniges Eruptivgestein aus Diallag und Plagioklas, mit akzessorischem Titaneisen, Apatit, Enstatit etc., auch mit Olivin (Olivin G.), massiges, in mächtigen Stöcken zwischen Graniten, Gneisen und Glimmerschiefern auftretendes Gestein;… …   Kleines Konversations-Lexikon

  • gabbro — [gab′rō] n. [It < L glaber, bare: see GLABROUS] any of a group of usually dark, coarsegrained, igneous rocks, composed chiefly of pyroxene and plagioclase …   English World dictionary

  • Gabbro — Handstück eines Gabbro Star Galaxy: Ein Gabbro aus Indien. Muster ca. 25×15cm …   Deutsch Wikipedia


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