Amphibolite Rock Type, Formation, Occurrence & Uses

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Amphibolite is a dark-colored, weekly-foliated metamorphic rock that contains plagioclase feldspar and amphibole of the hornblende group. The amphibole is usually green, brown, or black. The rock may also contain metamorphic minerals like garnet, wollastonite, andalusite, staurolite, kyanite, biotite, epidote, and sillimanite. Quartz, magnetite, and calcite are also present in trace amounts in some rocks.

AmphiboliteAmphibolite from Cape Cod, Massachusetts
Amphibolite from Cape Cod, Massachusetts

Amphibolite Formation

Amphibolite is usually found at convergent plate boundaries, at regions where heat and pressure cause metamorphism. It is produced through the metamorphism of mafic igneous rocks such as basalt and gabbro. It is also formed due to the metamorphism of clay-rich sedimentary rocks like marl or graywacke. The metamorphism may flatten and elongate the mineral grains to produce a schistose texture.

Amphibolite rocks erode over time due to wind, sea, glacier, and chemical erosion.

Where is Amphibolite Found?

Amphibolite is a common rock and is found in many countries across the world. Its deposits are located in areas where mountains have formed. Almost all continents have vast amphibolite deposits except Antarctica. The chemical makeup may vary from one deposit to another, but its uses remain the same. It is usually found in places where basalt is found.

The rock originally begins as an igneous rock, but the metamorphism makes it a metamorphic rock. The rock base is exposed to water-borne minerals that combine to form a new rock.

Garnet-bearing amphibolite from Val di Fleres, Italy
Garnet-bearing amphibolite from Val di Fleres, Italy
Garnet amphibolite, sold as "Nordic Sunset Granite", reportedly from Murmansk area
Garnet amphibolite, sold as "Nordic Sunset Granite", reportedly from Murmansk area

Amphibolite Uses

Amphibolite’s major use is in the construction industry. Amphibolite is harder than limestone and heavier than granite, making the stone more durable than these two.

It is often used while building homes due to its dark and appealing texture. It can be polished to give a neat and clean look. Some attractive pieces are used to make fancy countertops. Amphibolite is often sold as one of the many types of black granite in the market.

Some rocks can be cut and polished to be used as jewelry item because it produces a shimmer effect.

Higher-quality amphibolite is cut and polished for architectural use. It is often used as a facing stone, floor tile, and panels. It is also used commercially in cemetery makers, commemorative tablets, and creating artwork.

Amphibolite is quarried and crushed to be used as an aggregate in highway construction and a ballast stone in railroad construction. It is cut to be used as a dimension stone.

Amphibolite was frequently used in the Neolithic age to make Adze. An adze is an ancient cutting tool similar to an axe.

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