Amphibolite
An amphibolite is a rock composed mainly of ampbibole (as hornblende) and plagioclase feldspars, with little or no quartz. It is typically dark-colored and heavy, with a foliated or schistose (flaky) structure. The small flakes of black and white in the rock often give it a salt and pepper appearance.
Although the rock-type is found in both unmodified igneous versions and as metamorphic rocks, traditionally only the metamorphosed form was called amphibolite. In modern sources this distinction is reduced and the name is sometimes applied to rocks of both origins.
The parent rock of amphibolite are basalts and other mafic igneous rocks. It forms by regional metamorphism along convergent plate boundaries.