Gabbro is widely used as crushed stone for concrete aggregate, road base material, and railroad ballast. Gabbro can be formed as a massive intrusion by crystallization of pyroxene and plagioclase, or as alternating light plagioclase feldspar and dark clinopyroxene layer. 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). Gabbro, any of several medium- or coarse-grained rocks that consist primarily of plagioclase feldspar and pyroxene.Essentially, gabbro is the intrusive (plutonic) equivalent of basalt, but whereas basalt is often remarkably homogeneous in mineralogy and composition, gabbros are exceedingly variable.Gabbros are found widely on the Earth and on the Moon as well. How did it form? Gabbro Gabbro is a dense, mafic intrusive rock. Gabbro formation took place millions of years ago. Gabbro is a coarse-grained igneous rock that forms when iron-rich magma cools slowly deep within the Earth. It is very similar to the fast cooling, extrusive basalt, as they both are formed from mafic magmas that contain dark-colored minerals such as pyroxene, plagioclase, amphibole, and olivine. Gabbro Composition. Gabbro is a large group of dark, coarse-grained, igneous rocks.They are chemically equivalent to basalt.The rocks are plutonic, formed when molten magma is trapped under the Earth's surface and cools into a crystalline mass.. Gabbro can also be gray or light green. There are a variety of Gabbro Uses and the Gabbro Reserves are found in many countries around the world. Gabbro is an intrusive igneous rock, meaning that it forms from the solidification of magma within the earth.Intrusive igneous rocks are medium- to coarse-grained because they cool slowly over time. Gabbro is a large group of dark, mafic igneous rocks that are chemically similar to basalt. The presence of gabbro in North Carolina is evidence of the divergent boundary that once caused ancient supercontinents to split up. The rocks in the earth’s crust continuously undergo changes in their composition which leads to formation of other rocks. Mafic magmas, formed in Earth’s upper mantle, sometimes contain significant amounts of periodot, garnet (grossular), and diamond known to form at great depths. Gabbro is a strange name that most people aren't familiar with, much less how it is formed. Gabbro (/ ˈ É¡ æ b r oʊ /) is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. It generally occurs as batholiths and laccoliths and is often found along mid-ocean ridges or in ancient mountains composed of compressed and uplifted oceanic crust. Gabbro Formation. It is made up of plagioclase feldspar and pyroxene. Gabbro is the plutonic equivalent of basalt. Definition – Gabbro (/ˈɡæbroʊ/) is a phaneritic (coarse-grained), is an intrusive igneous rock that forms from the result of slow cooling of magma inside of a volcano. Long belts of gabbroic intrusions are typically formed at proto-rift zones and around ancient rift zone margins, intruding into the rift flanks. Gabbro is a medium-grained, ultramafic igneous rock. Gabbro is sometimes called “black granite” for it too is coarse-grained, but a large proportion of iron-bearing minerals make gabbro heavier and dark colored. If olivine is present, it shows the dark olivine layers as well. Gabbro is a typically dark colored, large-crystal igneous rock that forms from the slow cooling and crystallization of magmas below the Earth's surface. A thin layer of rocks at or above the oceanic crust are the basalts. 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