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Home » Rocks » Metamorphic Rocks » Amphibolite

Amphibolite


A metamorphic rock composed primarily of amphibole minerals and plagioclase feldspar



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 silimanite. 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.


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 a 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, 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.


IGNEOUS ROCKS
Andesite
Andesite
Basalt
Basalt
Quartz Diorite
Diorite
Gabbro
Gabbro
Granite
Granite
Obsidian
Obsidian
Pegmatite
Pegmatite
Peridotite
Peridotite
Pumice
Pumice

Rhyolite
Rhyolite

Scoria
Scoria

Welded Tuff
Tuff

METAMORPHIC ROCKS
Amphibolite
Amphibolite
Gneiss
Gneiss
Hornfels
Hornfels
Marble
Marble
Novaculite
Novaculite

Phyllite
Phyllite

Quartzite
Quartzite

Muscovite Schist
Schist

Slate
Slate

Soapstone
Soapstone

   
SEDIMENTARY ROCKS
Breccia
Breccia
Chert
Chert
Anthracite Coal
Coal
Conglomerate
Conglomerate
Dolomite
Dolomite
Flint
Flint
Hematite Iron Ore
Iron Ore
Limestone
Limestone
Oil sand
Oil Sand
Oil shale
Oil Shale
Halite Rock Salt
Rock Salt
Sandstone
Sandstone
Shale
Shale
Siltstone
Siltstone
   



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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.




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.


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