amfibolia

Amfibolia, or amphibolite in English, is a metamorphic rock characterized by a predominant content of amphibole minerals—most commonly hornblende—together with plagioclase feldspar. The rock is typically medium to coarse-grained and may be massive or display a clear metamorphic foliation produced by mineral alignment.

Amphibolite forms during regional metamorphism of mafic to pelitic precursor rocks under amphibolite facies conditions, roughly 500–750°C and moderate to high pressures. When plagioclase and amphibole crystallize together, they yield a dark, dense rock. Quartz, if present, is usually minor.

Dominant minerals are amphibole (often hornblende) and plagioclase feldspar, with accessory minerals such as magnetite, biotite, chlorite, and epidote. The metamorphic texture is typically schistose or gneissic, resulting from the preferred orientation of elongated amphibole crystals and platy minerals during deformation.

Amphibolites are widespread in ancient continental crust and commonly form from mafic volcanic rocks or gabbric protoliths, as well as from metamorphosed pelitic rocks where fluids facilitate metamorphism. They occur in mountain belts and shield areas as units within greenschist to granulite terrains. Their mineralogy records metamorphic conditions and tectonic processes, and they may host asbestos-related minerals in tremolite-actinolite-rich varieties, a factor considered in handling and use.

Name-wise, the term amphibolite reflects the prominence of amphibole minerals in the rock. In some languages, the corresponding term for this rock type is amfibolia.