(redirected from gabbroic)
Also found in: Dictionary, Thesaurus.


see basaltbasalt
, fine-grained rock of volcanic origin, dark gray, dark green, brown, reddish, or black in color. Basalt is an igneous rock, i.e., one that has congealed from a molten state.
..... Click the link for more information.
The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



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.


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.


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.
References in periodicals archive ?
Such a mechanism accounts for the generation of voluminous bimodal (gabbroic and granitic) magmatism represented by the Bocabec, Utopia, Welsford, Jake Lee Mountain, Parks Brook, and Wellington Lake plutons lasting over a period of about 13 million years (Fig.
The calc-alkaline gabbroic intrusions, which are mainly concentrated in the western SCS (Franco and Garcia de Figuerola, 1986; Franco and Sanchez-Garcia, 1987), are small (usually < 1 km in length) Variscan post-tectonic plutons with ages mainly in the range 305-300 Ma (Zeck et al., 2007; Villaseca et al., 2011).
One key difference was that archaea were absent in the gabbroic layer.
Mineralisation occurs as several stacked lenses within a sequence of foliated sheet like gabbroic intrusive units and is associated with quartz veining and sulphide alteration between two strike parallel shear zones.
Surface mapping and geophysics have identified the Geordie East and Geordie North zones, which are both in excess of one km in length and are made up of gabbroic rocks similar to the Geordie Lake deposit.
Geochemically, these dolerites exhibit sub-alkalic, metaluminous, tholeitic to alkalic basalt character and fall in gabbroic category.
Most people know about the sinking of the Titanic on its maiden voyage in 1912; relatively few people know that 149 of the 150 victims buried in three cemeteries in Halifax, Nova Scotia, lie under petrologically identical gabbroic headstones (Fig.