amphiboliet

Amphiboliet, or amphibolite in English, is a metamorphic rock dominated by the mineral assemblage hornblende (an amphibole) and plagioclase. The rock may also contain quartz, biotite, magnetite, and accessory minerals. Its characteristic dark color and foliated to schistose texture reflect the alignment of minerals during metamorphism. Grain size can range from millimeters to centimeters.

The protoliths of amphiboliet are mafic to ultramafic igneous rocks, such as basalt, gabbro, or diorite, that have undergone metamorphism. The formation involves metamorphic reactions that stabilize hornblende and plagioclase at higher temperatures and pressures than greenschist facies, resulting in the amphibolite facies mineral assemblage. Amphiboliet commonly exhibits a pronounced foliation or banding derived from preferred mineral orientation.

Amphibolite facies corresponds to intermediate to high-grade metamorphism, typically at temperatures around 500–750°C and pressures from a few to over ten kilobars, depending on depth and tectonic setting. The result is a relatively dense, durable rock that records the metamorphic history of its host rock.

Occurrence and use: Amphiboliet is widespread in many orogenic regions where mafic crust has undergone metamorphism, including ancient cratons and mountain belts. Economically, it is mined as a source of hornblende and sometimes used locally as a decorative or dimension stone and for aggregate, though its practical use varies by region.

In summary, amphiboliet is a hornblende-plagioclase–rich metamorphic rock formed from mafic protoliths under amphibolite facies conditions, notable for its dark, foliated texture and its role in revealing metamorphic histories.