metamorphic
Amphibolite / Biotite Schist
Amphibolite (rich in Hornblende and Plagioclase feldspar)
Hardness around 5.5-6 on Mohs scale. Dark charcoal gray to black color with fine glistening white speckles (feldspar/quartz) and sparkling reflective mica/amphibole flakes. Foliated to sub-foliated metamorphic texture with a vitreous to pearly luster.
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Physical properties
Hardness around 5.5-6 on Mohs scale. Dark charcoal gray to black color with fine glistening white speckles (feldspar/quartz) and sparkling reflective mica/amphibole flakes. Foliated to sub-foliated metamorphic texture with a vitreous to pearly luster.
Formation & geological history
Formed through regional metamorphism of mafic igneous rocks (such as basalt or gabbro) or clay-rich sedimentary rocks under high temperatures and moderate-to-high pressures during mountain-building events.
Uses & applications
Used as crushed stone for road base, railway ballast, and construction aggregate. Dimension stone quality pieces are sometimes polished for counter tops or architectural facings.
Geological facts
Amphibolites make up significant portions of ancient continental shields and mountain belts like the Appalachian and Alpine chains, offering key insights into tectonic history.
Field identification & locations
Look for a dark, dense rock with aligned elongated dark minerals (hornblende) interspersed with fine white feldspar grains that sparkle under direct light. Common in metamorphic terranes worldwide.
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