Gabbro
Igneous rocks form by the cooling & crystallization of hot, molten rock (magma & lava). If this happens at or near the land surface, or on the seafloor, they are extrusive igneous rocks. If this happens deep underground, they are intrusive igneous rocks. Most igneous rocks have a crystalline texture, but some are clastic, vesicular, frothy, or glassy.
Gabbro is an intrusive igneous rock - it is the dominant rock in Earth’s lower oceanic crust. Gabbro has a mafic chemistry. Mafic igneous rocks are generally dark-colored, have 45-52% silica (= SiO2 chemistry) (mafic has also been defined as 45 to 55% silica), are rich in iron (Fe), magnesium (Mg), & calcium (Ca), and are dominated by the minerals plagioclase feldspar and pyroxene.
Gabbro has the same chemistry and mineralogy as basalt, but is coarsely crystalline - it has a phaneritic texture (all or almost all crystals are between 1 mm and 1 cm in size each). Phaneritic texture forms by relatively slow cooling of magma deep underground. Gabbros are dominated by the minerals plagioclase feldspar (grayish) and pyroxene (black). The bluish-colored areas in the above photo are an artifact from the scanner light.
Gabbro
Igneous rocks form by the cooling & crystallization of hot, molten rock (magma & lava). If this happens at or near the land surface, or on the seafloor, they are extrusive igneous rocks. If this happens deep underground, they are intrusive igneous rocks. Most igneous rocks have a crystalline texture, but some are clastic, vesicular, frothy, or glassy.
Gabbro is an intrusive igneous rock - it is the dominant rock in Earth’s lower oceanic crust. Gabbro has a mafic chemistry. Mafic igneous rocks are generally dark-colored, have 45-52% silica (= SiO2 chemistry) (mafic has also been defined as 45 to 55% silica), are rich in iron (Fe), magnesium (Mg), & calcium (Ca), and are dominated by the minerals plagioclase feldspar and pyroxene.
Gabbro has the same chemistry and mineralogy as basalt, but is coarsely crystalline - it has a phaneritic texture (all or almost all crystals are between 1 mm and 1 cm in size each). Phaneritic texture forms by relatively slow cooling of magma deep underground. Gabbros are dominated by the minerals plagioclase feldspar (grayish) and pyroxene (black). The bluish-colored areas in the above photo are an artifact from the scanner light.