Amphibolite is the name given to a rock consisting mainly of hornblende, the use of the term restricted to rocks that have been metamorphosed.  A holocrystalline plutonic igneous rocks composed primarily of hornblende is a hornblendite. Rocks with greater than 90% amphibole and which have a feldspar groundmass may be termed lamprophyres. Amphibolite is a grouping of rocks composed mainly of amphibole (as hornblende) and plagioclase feldspars, with little or no quartz. It is typically dark-colored and heavy, with a weakly foliated or schistose texture. The intermixed small mineral flakes of black hornblende and white plagioclase in the rock often give it a salt-and-pepper appearance. Amphibolites need not be derived from metamorphosed mafic rocks. Since metamorphism gives rise to minerals based entirely upon the chemistry of the protolith, certain shaly limestones and volcaniclastics may metamorphose into an amphibolite. Deposits containing dolomite and siderite also readily yield amphibolites such as tremolite-schists and grunerite-schists, especially where there has been a certain amount of contact metamorphism by adjacent granitic intrusions. Metamorphosed basalts are the parents of orthoamphibolites and other chemically appropriate lithologies give rise to paraamphibolites.
Photographed by Michael P. Klimetz

Gallatin Gateway

Gallatin County
MONTANA
Amphibolite
Photographed by Michael P. Klimetz


Proterozoic
Ramapo Fault Zone

Albany Post Road
Garrison

Putnam County
NEW YORK
Photographed by Michael P. Klimetz


Proterozoic
Ramapo Fault Zone

Albany Post Road
Garrison

Putnam County
NEW YORK
Photographed by Michael P. Klimetz


Proterozoic
Ramapo Fault Zone

Albany Post Road
Garrison

Putnam County
NEW YORK
Photographed by Michael P. Klimetz


Proterozoic
Ramapo Fault Zone

Albany Post Road
Garrison

Putnam County
NEW YORK
Photographed by Michael P. Klimetz


Proterozoic
Ramapo Fault Zone

Albany Post Road
Garrison

Putnam County
NEW YORK
Photographed by Michael P. Klimetz


[Garnet-Hornblende Amphibolite]


Proterozoic
Baltimore Gneiss

Hollofield

Baltimore County
MARYLAND
Photographed by Michael P. Klimetz


[Garnet-Hornblende Amphibolite]


Proterozoic
Baltimore Gneiss

Hollofield

Baltimore County
MARYLAND
Photographed by Michael P. Klimetz


[Hornblende Amphibolite with Disseminated Magnetite]


Proterozoic

Breakneck Ridge
Hudson Highlands

Putnam County
NEW YORK
Photographed by Michael P. Klimetz


[Hornblende Amphibolite with Disseminated Magnetite]


Proterozoic

Breakneck Ridge
Hudson Highlands

Putnam County
NEW YORK
Photographed by Michael P. Klimetz


[Hornblende Amphibolite with Disseminated Magnetite]


Proterozoic

Breakneck Ridge
Hudson Highlands

Putnam County
NEW YORK
Photographed by Michael P. Klimetz


[Hornblende Amphibolite with Disseminated Magnetite]


Proterozoic

Breakneck Ridge
Hudson Highlands

Putnam County
NEW YORK
Photographed by Michael P. Klimetz


[Hornblende Amphibolite with Almandine Garnet Xenocryst]

Clay County
NORTH CAROLINA
Photographed by Michael P. Klimetz


[Hornblende Amphibolite with Almandine Garnet Xenocryst]

Clay County
NORTH CAROLINA
Photographed by Michael P. Klimetz


[Hornblende Amphibolite with Almandine Garnet Xenocryst]

Clay County
NORTH CAROLINA