Gabbro (/ˈɡæb.roʊ/) is a mafic intrusive igneous rock formed by the slow cooling of magnesium- and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slowly cooling coarse-grained gabbro is chemically equivalent to rapidly cooling fine-grained basalt. Much of the Earth's oceanic crust is composed of gabbro, formed at mid-ocean ridges. Gabbro also occurs as plutons associated with continental volcanism. Because of its variable nature, the term gabbro can be loosely applied to a wide range of intrusive rocks, many of which are simply "gabbroids". Roughly speaking, gabbro is to basalt as granite is to rhyolite. The term "gabbro" was used in the 1760s to describe a set of rock types that were found in the ophiolites of the Apennine Mountains in Italy. It was named after Gabbro, a village near Rosignano Marittimo in Tuscany. Then, in 1809, the German geologist Christian Leopold von Buch used the term more restrictively in his description of these Italian ophiolite rocks. He assigned the name "gabbro" to rocks that geologists today would more strictly call "metagabbro" (metamorphosed gabbro).

Gabbro is much less common than the more silica-rich intrusive rocks in the Earth's continental crust. Gabbros and gabbroids occur in some batholiths, but these rocks are relatively minor constituents of these very large intrusions because their iron and calcium content usually makes gabbroic and gabbroic magmas too dense to be buoyant. However, gabbro is an integral part of the oceanic crust and occurs in many ophiolite complexes as gabbro beds beneath layered dike complexes and above ultramafic rocks derived from the Earth's mantle. These layered gabbros may have formed from relatively small but long-lived magma chambers located beneath mid-ocean ridges.

Layered gabbroids are also characteristic of lopoliths, which are large saucer-shaped intrusions that are mostly Precambrian in age. (The Precambrian is the earliest part of Earth's geological history, preceding the beginning of the Cambrian Period. The Precambrian period is currently estimated to span over 2,900 million years, from the earliest known geological formations, about 3,500 million years old, to the beginning of the Cambrian period, about 570 million years ago.

Prominent examples of lopoliths include the Bushveld Complex in South Africa, the Muskoka Intrusion in the Northwest Territories of Canada, the Rum Layered Intrusion in Scotland, the Stillwater Complex in Montana, and the layered gabbroids near Stavanger, Norway.[25] Gabbroids are also present in deposits associated with alkaline volcanism associated with continental rifting.

Gabbros often contain large amounts of chromium, nickel, cobalt, gold, silver, platinum, and copper sulfides.[27][28][29] For example, the Merensky Reef is the world's most important source of platinum.

Gabbro is widely used in the construction industry under the trade name black granite. However, gabbro is a hard material that is difficult to work with, limiting its uses.

The term "indigo gabbro" is used as a general name for a mineralogically complex type of rock, often found in shades of black and purple-gray. It is mined in central Madagascar for use as a semi-precious stone. Indigo gabbro can contain a variety of minerals, including quartz and feldspar. Reports say that the rock's dark matrix is ​​composed of mafic igneous rock, but it is unclear whether it is basalt or gabbro.

•Chemical Description: Rock.

•Lightfastness – 8

•Alkali resistance:5

•Lime resistance:5

•Acid resistance:5

•ColorIndex basalt analog, PB128

•Lens

•Suitability Acrylic, Fresco, Ceramics, Oil, Tempera, Watercolor / Gouache, Silicate binder, Cement / Plaster

•Color brownish-gray

•Form powder

•Hiding power average