Gabbro specimen.

Gabbro 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. Image File history File linksMetadata Gabro. ... Image File history File linksMetadata Gabro. ... Volcanic rock on North America Plutonic rock on North America Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Basalt Basalt is a common gray to black volcanic rock. ... Pluton redirects here. ... Magma is molten rock located beneath the surface of the Earth (or any other rocky planet), and which often collects in a magma chamber. ... Earth (often referred to as The Earth) is the third planet in the solar system in terms of distance from the Sun, and the fifth in order of size. ...

The vast majority of the Earth's surface is underlain by gabbro within the oceanic crust, produced by basalt magmatism at mid-ocean ridges. Age of oceanic crust Oceanic crust is the part of Earths lithosphere which underlies the ocean basins. ... A mid-ocean ridge or mid-oceanic ridge is an uplifting of the ocean floor that occurs when convection currents beneath the ocean bed force magma up where two tectonic plates meet at a divergent boundary. ...

Petrology

Gabbro is an extrusive melting lava. Gabbro is dense, greenish or dark-colored and contains varied percentages of pyroxene, plagioclase, amphibole, and olivine (olivine gabbro when olivine is present in large quantities) The pyroxene is mostly clinopyroxene, small amounts of orthopyroxene my be present. If the amount of Orthopyroxene is substantially greater than the amount of clinopyroxene, the rock is then a Norite. Quartz gabbros are also known to occur and are probably derived from magma that was saturated with silica. On the other hand, essexites represent gabbros whose parent magma had an insufficiency of silica, resulting in the formation of nepheline. Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... Lunar Ferroan Anorthosite #60025 (Plagioclase Feldspar). ... For the logical fallacy, see Amphibology. ... Olivine The mineral olivine is a magnesium iron silicate with the formula (Mg,Fe)2SiO4 in which the ratio of magnesium and iron varies between the two endmembers of the series: forsterite (Mg-rich) and fayalite (Fe-rich). ... Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... Norite is a mafic intrusive igneous rock composed largely of the calcium rich plagioclase labradorite and hypersthene with olivine. ... Quartz is amongst one of the most common minerals in the Earths continental crust. ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ... Essexite is a dark gray or black igneous rock. ... Nephelite, also called nepheline, is a feldspathoid -- a silica-undersaturated aluminosilicate, Na,K) AlSiO4, that occurs in intrusive and volcanic rocks undersaturated with silica, and in their pegmatites. ...

Gabbro is generally coarse grained, with crystals in the size range of 1 mm or greater. Finer grained equivalents of gabbro are called diabase, although the vernacular term microgabbro is often used when extra descriptiveness is desired. Gabbro may be extremely coarse grained to pegmatitic, and some pyroxene-plagioclase cumulates are essentially coarse grained gabbro, although these may exhibit acicular crystal habits. Diabase is a mafic, holocrystalline, igneous rock equivalent to volcanic basalt or plutonic gabbro. ... In geology a cumulate is an igneous rock formed by the accumulation of crystals from a magma. ...

Gabbro is usually equigranular in texture, although it may be porphyritic at times, especially when plagioclase has grown earlier than the groundmass minerals.

Distribution

Gabbro can be formed as a massive uniform intrusion or as part of a layered ultramafic intrusions as a cumulate rock formed by settling of pyroxene and plagioclase. Cumulate gabbros are more properly termed pyroxene-plagioclase cumulate. Examples Bushveld Igneous Complex Windimurra Intrusion Giles Complex intrusions Category: ... In geology a cumulate is an igneous rock formed by the accumulation of crystals from a magma. ...

Gabbro is an essential part of the oceanic crust, and can be found in many ophiolite complexes as parts of zones III and IV (sheeted dyke zone to massive gabbro zone). Long belts of gabbroic intrusions are typically formed at proto-rift zones and around ancient rift zone margins, intruding into the rift flanks. Mantle plume hypotheses may rely on identifying similar massive gabbro intrusions and coeval basalt volcanism. Ophiolites are sections of oceanic lithosphere that have been uplifted or emplaced to be exposed within continental crustal rocks. ... In geology, a rift is a place where the Earths lithosphere is expanding. ... A mantle plume is an upwelling of molten rock within the Earths (or another planets) mantle. ... Basalt Basalt is a common gray to black volcanic rock. ...

Uses

Gabbro often contains valuable amounts of chromium, nickel, cobalt, gold, silver, platinum, and copper sulfides. General Name, Symbol, Number chromium, Cr, 24 Chemical series transition metals Group, Period, Block 6, 4, d Appearance silvery metallic Atomic mass 51. ... General Name, Symbol, Number nickel, Ni, 28 Chemical series transition metals Group, Period, Block 10, 4, d Appearance lustrous, metallic Atomic mass 58. ... General Name, Symbol, Number cobalt, Co, 27 Chemical series transition metals Group, Period, Block 9, 4, d Appearance metallic with gray tinge Atomic mass 58. ... General Name, Symbol, Number gold, Au, 79 Chemical series transition metals Group, Period, Block 11, 6, d Appearance metallic yellow Atomic mass 196. ... General Name, Symbol, Number silver, Ag, 47 Chemical series transition metals Group, Period, Block 11, 5, d Appearance lustrous white metal Atomic mass 107. ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Atomic mass 195. ... General Name, Symbol, Number copper, Cu, 29 Chemical series transition metals Group, Period, Block 11, 4, d Appearance metallic brown Atomic mass 63. ... The term sulfide (sulphide in British) refers to several types of chemical compounds containing sulfur in its lowest oxidation number of -2. ...

Ocellar varieties of gabbro are often used as ornamental facing stones, paving stones and it is also known by the trade name of 'black granite', which is a popular type of headstone used in funerary rites.

Etymology

Gabbro was named by the German geologist Christian Leopold von Buch after a town in the Italian Tuscany region. Essexite is named after the type locality in Essex, Wales. Christian Leopold Freiherr von Buch (* April 26th 1774 in Stolpe (Brandenburg), † March 4th 1853 in Berlin) was a German geologist and is remembered as one of the most important contributors to geology in the first half of the nineteenth century. ... Tuscany (Italian Toscana) is a region in North-West Italy, bordering on Latium to the south, Umbria and Marche to the east, Emilia-Romagna and Liguria to the north, and the Tyrrhenian Sea to the west. ...

See also

• Igneous rocks
• Cumulate rocks

Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... In geology a cumulate is an igneous rock formed by the accumulation of crystals from a magma. ...

External links

• Ocean Drilling Program Gabbro Petrology
• Scientists Find the Elusive Gabbro