Gabbro is an intrusive igneous rock, coarse grained, dark coloured and consists mainly of calcium rich plagioclase feldspar and clinopyroxene. Minor amount of olivine, biotite, magnetite, apatite, ilmenite and orthopyroxene can also be the constituent mineral. Gabbro is very low on silica content thus have little to no quartz content.
The colour of gabbro is black or dark green which is by the constituent mineral content.
Gabbro extrusive equivalent rock is basalt which is an extrusive igneous rock the only difference is the grain size as basalt is extrusive which cools rapidly giving fine grained texture.
Petrology of Gabbro
Gabbro is thick, greenish or dim hued and contains pyroxene, plagioclase, and minor measures of amphibole and olivine.
The pyroxene substance is for the most part clinopyroxene, by and large augite, yet little measures of orthopyroxene may likewise be available. In the event that the measure of orthopyroxene is over 95% of the aggregate pyroxene content (5% or less clinopyroxene content), then the stone is named norite. Then again, gabbro has over 95% of its pyroxenes as the monoclinic clinopyroxene/s. Moderate rocks are named gabbro-norite. The calcium rich plagioclase feldspar (labradorite-bytownite) and pyroxene content shift between 10% - 90% in gabbro. In the event that over 90% plagioclase is available, then the stone is an anorthosite. In the event that then again, the stone contains over 90% pyroxenes (frequently both are available), it is named pyroxenite. Gabbro may likewise contain little measures of ("olivine gabbro" if generous measure of olivine is available), amphibole and biotite. The quartz content in gabbro is under 5% of aggregate volume. 'Quartz gabbros' or monzogabbros are additionally known to happen, for instance the cizlakite at Pohorje in northeastern Slovenia, and are most likely gotten from magma that was over-immersed with silica. Essexites speak to gabbros whose parent magma was under-immersed with silica, bringing about the development of the feldspathoid minerals nepheline, cancrinite, and sodalite as embellishment minerals instead of quartz. (Silica immersion of a stone can be assessed by standardizing mineralogy). Gabbros contain minor sums, regularly a couple percent, of iron-titanium oxides, for example, magnetite, ilmenite, and ulvospinel.
Gabbro is for the most part coarse grained, with gems in the size scope of 1 mm or more prominent. Better grained counterparts of gabbro are called diabase (otherwise called dolerite), in spite of the fact that the term microgabbro is frequently utilized when additional distinction is sought. Gabbro might be amazingly coarse grained to pegmatitic, and some pyroxene-plagioclase cumulates are basically coarse grained gabbro, some may display acicular precious stone propensities.
Gabbro is typically equigranular in surface, in spite of the fact that it might be porphyritic now and again, particularly when plagioclase oikocrysts have become sooner than the groundmass minerals.
Distribution of Gabbro
Gabbro can be framed as a gigantic, uniform interruption through in-situ crystallization of pyroxene and plagioclase, or as a major aspect of a layered interruption as a cumulate shaped by settling of pyroxene and plagioclase. Cumulate gabbros are all the more appropriately named pyroxene-plagioclase adcumulate.
Gabbro is a basic part of the maritime outside, and can be found in numerous ophiolite buildings as parts of zones III and IV (sheeted dyke zone to monstrous gabbro zone). Long belts of gabbroic interruptions are normally framed at proto-break zones and around antiquated crack zone edges, encroaching into the fracture flanks. Mantle crest theories may depend on recognizing mafic and ultramafic interruptions and contemporary basalt volcanism.
About all gabbros are found in plutonic bodies, however to confine the term (as the International Union of Geological Sciences, IUGS, proposes) just to plutonic rocks is wrong, since gabbro might be found as a coarse-grained inside facies of certain thick magmas. It is ideal to construct a stone definition with respect to spellbinding qualities of the stone as opposed to how or where it was framed.
The oceanic crust deep inside earth crust is made up of gabbro due to it slow cooling rate, the grains are coarser. At the surface of the ocean crust, basalt is abundant which is an extrusive rock. The temperature at the surface is cooler compare to interior portion so basaltic grains will be finer.
Gabbro in continental crust
On the continent, gabbro can be found in thick lava flows of basaltic in nature where cooling rate is slower allowing crystals to grow larger. These can also be found where magma chamber feed the continental crust and when it dies the cooling rate will be enough to grow large crystal which will in turn make gabbro deposits.
Gabbro serving as ore
Gabbro have sometimes associated minerals which can be mined. Gabbro contains mineral ilmenite which can be mined for its titanium content and other can be mined for nickel, chromium or platinum.
Uses of gabbro
The most common use of gabbro is as a crushed stone or aggregate in construction projects as road construction. It can also be used as a brittle polish gabbro for cemetery markers, floor tiles, facing stone etc. It can also be used as a dimension stone.