metamorphic
Garnet amphibolite / Metamorphic Rock
Garnet Amphibolite (Hornblende - Almandine schist/gneiss)
Hardness 6-7.5 (Mohs), dark green to black hornblende matrix with reddish-brown almandine garnet inclusions, vitrous to dull luster, medium to coarse-grained texture, specific gravity 3.0-3.4.
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Physical properties
Hardness 6-7.5 (Mohs), dark green to black hornblende matrix with reddish-brown almandine garnet inclusions, vitrous to dull luster, medium to coarse-grained texture, specific gravity 3.0-3.4.
Formation & geological history
Formed under regional metamorphism at high pressures and temperatures (medium to high grade metamorphic conditions) from the alteration of mafic igneous rocks like basalt or gabbro.
Uses & applications
Used as crushed stone in construction, decorative dimension stone, and for geological educational specimens. High-grade garnets inside may be used as industrial abrasives or gems.
Geological facts
Amphibolites often record ancient tectonic collision zones where oceanic crust was subducted and metamorphosed deep within the Earth's crust before being uplifted.
Field identification & locations
Identified by the distinct contrast between dark green amphibole minerals (hornblende) and reddish almandine garnets. Commonly found in metamorphic terranes like the Appalachian Mountains and Scandinavian shield areas.
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