gabbro

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gabbro:

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.
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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.

gabbro

[′gab·rō]
(petrology)
A group of dark-colored, intrusive igneous rocks with granular texture, composed largely of basic plagioclase and clinopyroxene.

gabbro

Igneous rock similar to diorite, predominantly composed of ferromagnetic minerals with crystals visible to the eye; has the same mineral composition as basalt.
References in periodicals archive ?
More recently, it has been observed that differences in initial [epsilon]Hf values between zircon crystals from several gabbroic bodies are in accordance with the heterogeneity of whole-rock Sr-Nd isotopic data, and that within sample [epsilon]Hf variability also indicates that crustal assimilation and felsic magma hybridization occurred in some of these intrusions (Villaseca et al.
One key difference was that archaea were absent in the gabbroic layer.
Coronite structure of this sample, however, is rather exceptional among prevailing rock types of the gabbroic complex.
Tholeiitic basaltic flows and minor gabbroic stocks are exposed extensively in the southern peninsula area of Costa Rica (Fig.
The Radio Hill intrusion is elongated north-south and comprises a thick ultramafic zone overlying a thinner gabbroic zone.
Gold veins on the property are hosted in several rock types including Paleozoic meta-arenites, phyllites, cherts,and smeta-basalts all of which have been intruded by granodioritic and gabbroic intrusives of Triassic-Jurassic age.
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.
Petrological and geochemical data is consistent with the basaltic, doleritic and gabbroic intrusions comprising alkalic series signatures, characteristic of heterogeneous asthenospheric melting associated with ocean island basalt (OIB) magmatism.
Besides geological samples (volcanic and gabbroic igneous rocks, loose sediments, active and inactive hydrothermal precipitates, fault and fracture Latvians) have biological samples (biodiversity of pelagic and hydrothermal fauna, benthic larvae in the water column, colonies of sessile life forms, demersal fish) and hydrothermal fluids ( solutions and gases) are sampled from active outlets.
2005) in the San Miguel region, allowed the identification of a gabbroic body which has been mapped at semi-detailed scale (Fig.
According to the 'Ophiolite-Manifesto' (Anonymous, 1972), an ophiolitic suite corresponds to a distinctive assemblage of mafic to ultramafic rocks, from botton to top: ultramafic complex, gabbroic complex, mafic sheeted dike complex, mafic volcanic complex and associated rock types, including overlying sedimentary section.