metamorphic
Amphibolite
Hornblende–plagioclase amphibolite
AI-generated identification · may be incorrectTypically dark green-black with pale gray-white streaks, medium- to coarse-grained, and nonmetallic with a dull to weakly vitreous luster. Hardness is about 5–6 for amphibole and 6–6.5 for plagioclase; crystals commonly show amphibole cleavage but no obvious layering here.
Identified More metamorphic →
Explore Amphibolite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically dark green-black with pale gray-white streaks, medium- to coarse-grained, and nonmetallic with a dull to weakly vitreous luster. Hardness is about 5–6 for amphibole and 6–6.5 for plagioclase; crystals commonly show amphibole cleavage but no obvious layering here.
Formation & geological history
Forms when basaltic or gabbroic rocks undergo medium- to high-grade regional metamorphism, commonly during mountain building. The specimen’s precise age cannot be determined visually; amphibolites range from Archean to recent metamorphic belts.
Uses & applications
Used locally as crushed stone, aggregate, road material, and dimension stone; attractive polished pieces may be collected, though it is rarely a major gemstone material.
Geological facts
The light and dark pattern reflects interlocking plagioclase and dark amphibole, commonly hornblende. It can resemble gneiss, diabase, or serpentinite, but amphibolite generally lacks metallic shine and has a crystalline, granular texture.
Field identification & locations
Look for a dense dark rock with visible black amphibole and pale plagioclase, moderate heft, and no vesicles; a streak or thin-section test can confirm it. Common in metamorphic mountain belts worldwide, including the Appalachians, Canadian Shield, and Scandinavia.
More like this
