Home » Rocks » Metamorphic Rocks » Amphibolite

Amphibolite


A metamorphic rock composed primarily of amphibole minerals and plagioclase feldspar


Amphibolite

Amphibolite: Amphibolite is a coarse-grained metamorphic rock that has amphibole minerals such as the hornblende group as its primary ingredient. The specimen shown is about two inches (five centimeters) across.

What is Amphibolite?

Amphibolite is a coarse-grained metamorphic rock that is composed mainly of green, brown, or black amphibole minerals and plagioclase feldspar. The amphiboles are usually members of the hornblende group. It can also contain minor amounts of other metamorphic minerals such as biotite, epidote, garnet, wollastonite, andalusite, staurolite, kyanite, and sillimanite. Quartz, magnetite, and calcite can also be present in small amounts.




How Does Amphibolite Form?

Amphibolite is a rock of convergent plate boundaries where heat and pressure cause regional metamorphism. It can be produced through the metamorphism of mafic igneous rocks such as basalt and gabbro, or from the metamorphism of clay-rich sedimentary rocks such as marl or graywacke. The metamorphism sometimes flattens and elongates the mineral grains to produce a schistose texture.



Amphibolite

Amphibolite: Some amphibolites are greenish, as determined by the color of the amphibole minerals. This specimen is actually an igneous rock. Some geologists call an igneous rock composed primarily of amphibole minerals an amphibolite or "hornblendite." USGS image.

Uses of Amphibolite

Amphibolite has a variety of uses in the construction industry. It is harder than limestone and heavier than granite. These properties make it desirable for certain uses. Amphibolite is quarried and crushed for use as an aggregate in highway construction and as a ballast stone in railroad construction. It is also quarried and cut for use as a dimension stone.

Higher quality stone is quarried, cut, and polished for architectural use. It is used as facing stone on the exterior of buildings, and used as floor tile and panels indoors. Some of the most attractive pieces are cut for use as countertops. In these architectural uses, amphibolite is one of the many types of stone sold as "black granite."

Some amphibolite deposits, such as the one at Gore Mountain in the Adirondacks of New York, contain significant amounts of garnet. If enough garnet is present and of proper quality, the amphibolite can be mined and the garnet recovered for use as an abrasive.



Rock kit

Rock & Mineral Kits: Get a rock, mineral, or fossil kit to learn more about Earth materials.

More Rocks
  Tumbled Stones
  Quartzite
  Siltstone
  Fluorescent Minerals
  Rock Kits
  Difficult Rocks
  Rock Tumblers
  Hand Lens

geology store

More From Geology.com:


rock tumblers
Rock Tumblers - All about rock tumblers and rock tumbling. Read before you buy a tumbler.
World Globes
World Globes - A nice selection of globes for students, schools, homes and offices.
Gfeller Leather Cases
Gfeller Leather field cases, hammer holsters, lanyards, field belts, acid bottle cases, more.
Geologist Tools
Geologist Tools: Visit our store for a large selection of field and laboratory tools.
Homeowners Insurance
Homeowners Insurance usually does not cover the most common geologic hazards.
Tumbled Stones
Tumbled Stones: A bag of tumbled stones is like a colorful rock collection.
Red Beryl
Red Beryl is one of the rarest gems. Small amounts are mined at one locality in Utah.
Rocks on Mars
Rocks on Mars: Many of the rocks found on Mars are not very different from Earth rocks.