Microgabbro

Microgabbro is a fine-grained, dark-colored igneous rock that is a variety of gabbro. It is composed primarily of plagioclase feldspar and pyroxene, with lesser amounts of olivine and amphibole. Microgabbro is characterized by its small grain size, which is typically less than 1 millimeter in diameter. This fine-grained texture is a result of rapid cooling of magma, often in a submarine environment or in a shallow intrusion.

Microgabbro is commonly found in oceanic crust and is a major component of ophiolite complexes, which are sections of oceanic crust and upper mantle that have been obducted onto continental margins. It is also found in some continental settings, such as in the roots of large igneous provinces and in some layered intrusions.

The term "microgabbro" was first used by the geologist Hans Ramberg in 1919 to describe a fine-grained gabbro from the Skaergaard intrusion in Greenland. Since then, the term has been widely used in the geological literature to describe fine-grained gabbros from a variety of settings.

Microgabbro has a density of approximately 2.9 to 3.1 grams per cubic centimeter and a hardness of about 6 to 7 on the Mohs scale. It is typically dark gray to black in color, with a fine-grained texture that can be difficult to distinguish from other fine-grained igneous rocks, such as diabase and basalt. Microgabbro is often used as a construction material, particularly in the production of crushed stone and aggregate.