Gabbro

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gabbro

[′gab·rō]
(petrology)
A group of dark-colored, intrusive igneous rocks with granular texture, composed largely of basic plagioclase and clinopyroxene.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

gabbro

Igneous rock similar to diorite, predominantly composed of ferromagnetic minerals with crystals visible to the eye; has the same mineral composition as basalt.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Gabbro

 

magmatic rock of basal composition, containing approximately equal parts of basal plagioclase (labradorite, bytownite) and colored minerals (pyroxenes, less frequently amphibole and olivine) and mineral ores in small quantities. Strictly, gabbro consists of plagioclase and monoclinic pyroxene. Varieties of gabbro include norites of plagioclase and rhombic pyroxenes and troctolites of plagioclase and olivine. If the gabbro contains olivine together with pyroxene, the rock is called olivine gabbro. Gabbros rich in plagioclase (85-90 percent) are called plagioclasites. Among these are labradorites, whose plagioclases often possess a beautiful bluish or greenish play of colors. The chemical composition of gabbro is approximately 45-50 percent silica and up to 20 percent oxides of iron and magnesium. The color is black or dark green, sometimes mottled. Typical gabbros that have hardened at great depths are characterized by approximately identically-sized crystals of the light and dark minerals that constitute it; gabbro in small masses usually has an ophitic structure. (The plagioclase is in the form of well-formed crystals, and the dark minerals fill the interstices between the plagioclases.) The forms and spatial distributions of the gabbro are large laccoliths, lopoliths, dikes, and stocks. Dimensions of the formations reach enormous magnitudes. (For example, the Duluth massif in Canada covers an area up to 5,000 sq km.) In the USSR there are large massifs of gabbro in the Urals, the Ukraine, the Kola Peninsula, the Transcaucasus, and other regions; outside the USSR there are gabbro masses in the Republic of South Africa, France, Scotland (Great Britain), and other countries. When gabbro disintegrates, ferrous clays, ochers, and, less frequently, low-quality kaolins are formed. Gabbros sometimes contain masses of ore minerals and in such cases may be used as ores of copper, nickel, and titanium. Gabbros are often used as building or facing stone of great strength, for exterior and interior facing, predominantly in the form of polished slabs (for example, the columns of the Lenin Library in Moscow), and for manufacturing gravel and road-paving stone.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
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References in periodicals archive ?
However, perhaps the compositions reported here are just some universal standard for augite rims in gabbros, in which case the statistical similarities mean nothing in terms of establishing a connection between the Titanic headstones and Hanson quarry.
Forensic igneous petrology: Locating the source quarry for the "black granite" Titanic headstones in Halifax, Nova Scotia, Canada
Other studies on Iberian Variscan gabbros have also highlighted the existence of crustal contamination at shallow levels on the basis of whole-rock chemistry (e.g.
Mineral chemistry of late Variscan gabbros from central Spain: constraints on crystallisation processes and nature of the parental magmas
By studying thin slices of the gabbros under polarizing microscopes, the scientists identified substantial amounts of the mineral orthopyroxene, a magnesium silicate that was thought to be absent from the lower crust.
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Gabbros are created by the injection of basaltic melt from the underlying rising mantle and are regarded as formed by slow crystallization in a magma chamber.
Petrology and geochemistry of gabbros from the Muslim Bagh Ophiolite: implications for their petrogenesis and tectonic setting
Oceanic crust is generally composed of dark-colored rocks called basalt and gabbro. It is thinner and denser than continental crust, which is made of light-colored rocks called andesite and granite.
Unraveling the tapestry of ocean crust: scientists follow a trail of clues to reveal the magmatic trickles and bursts that create the seafloor
These intrusions are mostly post-kynematic with respect to the Hercynian deformation [8] and are characterised by the presence of both mafic and acid igneous rocks, ranging from olivine gabbros to alkaline granites'.
The Aguablanca discovery
Also in this south sector (Cordon del Portillo) there is a plutonic association of gabbros and tonalites to granodiorites, and a volcanic sequence of andesites and dacites to rhyodacites and rhyolites (Polanski, 1972).
Origin and provenance of igneous clasts from late Palaeozoic conglomerate formations (Del Raton and El Planchon) in the Andean Precordillera of San Juan, Argentina
Vein hydrothermal metamorphism of Jandaq ophiolitic Gabbros (NE Isfahan province), journal of science, Isfahan University, Iran, 30(1): 83-100.
The role of structural and petrological elements in mineralization of hontite and magnesite in Ashin-Naein
This diagram illustrates the bimodality of the Landry Brook pluton compared to the more continuous trends in the other two plutons; the Landry Brook gabbros may therefore represent part of an unrelated but coeval suite that appears to be tholeiitic based on the AFM diagram (Fig.
Precise age and petrology of Silurian-Devonian plutons in the Benjamin River--Charlo area, northern New Brunswick

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